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| GM82C765b 1 GM82C765b floppy disk subsystem controller general description the GM82C765b is a cmos lsi device which interfaces a host microprocessor to the floppy disk drive. it integrates the function of the formatter/controller, data separator. write precompensa tion, data rate selection, clock generation, high current output drivers, and ttl compatible schmitt trigger receivers. the GM82C765b consists of a microprocessor interface, a microsequencer and a disk drive interface. the host microprocessor interface of the GM82C765b supports a 12mhz, 286 microprocessor bus without the use of wait states. all inputs within host microprocessor are schmitt triggers, except for the data bus, xtal, and the host output sink 12ma. output drive capability is 20 lsttl load, allow ing direct interconnection to bus structures without the use of buffers or transceivers. on the disk drive interface, the GM82C765b includes data seperation that has been designed to address high performance error rate on floppy disk drives, and contains a ll the necessary logic to achieve classical 2nd order, type2, phase locked loop performance. write precompensation is included, in addition to the usual formatting, encoding, decoding, step motor control, and status sensing functions for pc/xt and pc/at ap plications, the device provides qualification of interrupt and dma requests. the disk drive interface of the GM82C765b connects directly to up to four drives. all drive - related inputs are schmitt triggers and the drive outputs are open drain, and sink 48 m a. the GM82C765b uses two clock inputs which provide the necessary signals for internal timing. a 16mhz oscillator controls the data rate of 500, 250 and 125kbits/sec, while a 9.6mhz oscillator controls the 300kbit/sec data rate used in pc/at designs. the two xtal oscillator circuits may be used for the 44 - pin plcc package, while ttl clock inputs must be provided when using the 40 - pin dip package. in the plcc version of the GM82C765b pins 17 and 40, which were not utilized in dip version of the GM82C765b, b ecame dchgen (disk change enable) and dchg (disk change) respectively. both are active low. dchgen is offered as an option for those designs that used the original GM82C765b part where dchg did not exist as direct into the chip. the GM82C765b has eight internal registers. the 8 bit main status register contains status information of the GM82C765b and may be accessed any time. another four status register under system control also give va rious status and error information. the control register provides support logic that latches the two lsbs used to select the desired data rate that controls internal clock generation. the operations register replaces the standard latched port used in flopp y subsystem. features * ibm p c compatible format (single and double density) ? floppy disk control and operations on chip ? in pc at mode, provides required signal qualification dma channel ? bios compatible and dual speed spindle drive support * integ rates formatter/controller/data separation, write precompensation, data rate selection, clock generation, and drive interface driv ers and receivers into one chip * multisector and multitrack transfer capability. * direct floppy disk drive interface wi th no buffers needed ? 48ma sink output drivers ? schmitt trigger line receivers * enhanced host interface: ? supports 12mhz, 286 u - processor ? capable of driving 20 lsttl load * address mark detection circuitary internal to floppy disk controller * on ch ip clock generation two ttl clock inputs for 40 - dip * two xtal oscillator circuits for 44 - quad, plcc * user programmable track stepping rate and head load/unload time * drivers up to four flo ppy or micro floppy disk drives * da ta transfer dma or non - dma mode * p arallel seek operations on up to four drives * in ternal power up reset circuitry * read/write access compatible register with 8 or 12mhz 286 mic roprocessor with 0 wait states. * dma timing corrected. * low power cmos, +5v supply
GM82C765b 2 pin configuration 1. pin descriptions (condinued on next page) pin no dip plcc mnemomic signal name i/o function 1 1 rd read i st control signal for transfer of data or status onto the data bus by the GM82C765b 2 2 wr write i control signal for latching data form the bus into the GM82C765b buffer register. 3 3 cs select chip st selected when 0 (low) allowing rd or wr operation from the host 4 4 a0 address line i st address line selecting data (=1) or status (=0) information (a0 = logic 0 during wr is illegal) 5 5 dack dma e acknowledg i st used by the dma controller to transfer data from the GM82C765b onto the bus. logical equivalent to cs and a0=1. in special or pc at mode, this signal is qualified by dmaen from the operation register. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 23 22 21 1 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3 1 32 33 34 35 36 37 38 39 40 41 42 43 44 ao dack tc db0 db1 db2 db3 db5 db6 db7 dma rst irq db4 rd wr cs rdd ldcr ldor vcc wp hdl mo2. ds4 vss pcval clk1 drv clk2 dbo idx troo hs we wd dirc step ds1 ds2 mo1, ds3 rpm, rwc dchg troo cack ldcr ldor wp rd cs hs wr idx vcc a0 tc db1 db2 db3 db4 db5 db6 db7 dma irq dchgen xt1 xt2 pcval xt1 drv xt2 rst rdd ds2 vss hdl dir step wd ds4., mo2 ds3. , mo1 GM82C765b GM82C765b pl GM82C765b 3 pin dip plcc menmo - mic signa l name i/o function 6 6 tc terminal count i st this signal indicates to GM82C765b that data transfer is complete. if dma operational mode is selected for command execution, tc will be qualified by dack , but not in the prog rammed i/o execution. in pc at or special mode, qualification by dack requires the operations mode, qualification by dack requires the operations resister signal dmaen to be logically true. note also that in pc at mode, tc will be qualified by dack , whether in dma or non - dma host operation. programmed i/o in pc at mode will cause an abnormal termination error at the completion of a command. 7 - 14 7 - 14 dbo thru db7 data bus 0 thru data bus 7 i/o bi 8 - bi t bi - directional, tri - state, data bus. d0 is the least significant bit (lsb). d7 is the most significant bit (msb) 15 15 dma direct memory access o bi dma request for byte transfer of data. in special or pc at mode, this pin is tristated, enabled by the d maen signal from the operation register. this pin is driven in the base mode. 16 16 irq interrupt request o bi interrupt request indicating the completion of command execution or data transfer requests (in non dma mode). normally driven in base mode. in s pecial or pc at mode, this pin is tri - stated, enabled by the dmaen signal from the operations resister. 17 dchgen disk change enable i st this input must be at logic = 0 to enable dchg input status at pin 40 to be placed on db7 during a rd = 0 of ldcr = 0. internal pull - up. 17 18 ldor load operations register i st address decode which enables the loading of the operations resister. internally gated with wr creates the strobe which latches the two lsbs from the data bus into the operation resister. 18 19 ldcr load cintrol register i st address decode which enables the loading of the control resister. internally gated with wr creates the strobe which latches the two lsrs from thedata bus into the control resi ster. 19 20 rst reset i st reset controller, placing microsequencer in idle. resets device outputs. puts in base mode, not pc at or special mode. 20 21 rdd disk read data i st this is the raw serial bi t stream from the disk drive. each falling edge of the pulses represents a flux transition of the encoded data. 22 2 xt 2 xtal o n xtal oscillator drive output for 44 pin plcc should be left floating if ttl inputs used at pin 23. 23 xt2 xtal2 i n xtal oscillator input used for non - standard data rates. it may be driven with a ttl level signal 21 clk2 clock2 i n ttl level clock input used for non - standard data rates is 9.6mhz for 300 kbs, and can only be selected from the control register. * xt2 (pin23) of 44 pin - plcc (condinued on next page) GM82C765b 4 22 24 drv drive type i st drive type input indicates to the device that a two - speed spindle motor is used if logic is o. in that case, the second clock input will never be select ed and must be grounded. 25 1 xi 1 xtal o st xtal oscillator drive output for 44 pin plcc should be left floating if ttl inputs used at pin 26. 26 xt1 xtal1 i n xtal oscillator input requiring 16mhz crystal. this osc illator is used for all standard data rates, and may be driven with a ttl level signal. 23 clk1 clock1 i n ttl level clock input is used to generate all internal timings for standard data rates. frequency must be 16mhz 0.1%, and may 40/60 or 60/40 duty cycle. * xt1 (pin 26) of 44 - plcc 24 27 pcval precompen - sation value i st precompensation value select input. this pin determines the amount of write precompensation used on the inner tracks of the diskette. logic 1 = 125ns, logic 0 = 187ns 25 28 hs head select o hcd high current drive (hcd) output selects the head (side) of the floppy disk that is being read or written. logic 1 = side 0. logic 0 = side 1. 26 29 we enable write o hcd this hcd output becomes true, active low, just prior to writing on the diskette. this allows current to flow through the write head. 27 30 wd data write o hcd this hcd output data write . ea ch failing edge of the encoded data pulse stream causes a flux transition on the media. 28 31 dirc direction o hcd this hcd output determines the direction of the head step motor. logic 1 = outward motion. logic 0 = inward motion. 29 32 step pulse step control o hcd this hcd output issues an active low pulse for each track to track movement of the head. 30 33 1 ds 1 select drive o hcd this hcd out put, when active low, is 1 select drive in pc at mode, enables the interface in disk drive. this signal comes from the operations register. in base or special mode, this output is #1 of the four decoded unit selects, as specified in the device comm and syntax. 31 34 vss ground ground 32 35 2 ds 2 select drive o hcd this hcd output, when active low, is 2 select drive in pc at mode, enables the interface in disk drive. this signal comes from the operations regist er. in base or special mode, this output is # 2 of the four decoded unit selects, as specified in the device command syntax. 33 36 1 mo , 3 ds 1 on motor 3 select drive o hcd this hcd output, when active low, is motor on enable for disk drive #1, in pc at mode. this signal comes from the operations register in the base or special mode, this output is #3 of the four decoded unit selects as specified in the device command syntax. GM82C765b 5 pin no dip plcc mnemomic signal name i/o function 34 37 2 mo , 4 ds 2 on motor 4 select drive o hcd this hcd output, when active low, is motor on enable for disk drive #2, in pc at mode. this signal comes fr om the operations reg. in the base or special mode, this output is #4 of the four decoded unit selects as specified in the device command syntax 35 38 hdl head loaded o hcd this hcd output, when acti ve low, causes the head to be loaded against the media in the selected drive. 36 39 rwc rpm reduced write , current s revolution minute per o h cd this hcd output, when active los, causes a reduced current write when bit density is increased toward the inner tracks, becoming active when tracks>28 are accessed. this condition is valid for base or special mode, and is indica tive of when write precompensation is necessary. in the pc at mode, this signal will be active when cr0=1 40 dchg disk change i st this st input senses status from the drive, indicating active low th at drive door is open or that the diskette has possibly changed since last drive selection. 37 41 wp write protected i st this schmitt trigger (st) input senses status from the disk drive, indicating ac tive low when a diskette is write protected 38 42 00 tr 00 track i st this st input senses status from disk drive indicating active low when the head is positioned over the outermost track, 00 track 39 43 idx index i st this st input senses status from the disk drive, indicating active low when the head is positioned over the beginning of a track marked by an index hole. 40 44 vcc +5v dc input power supply. note: n ? normal input, output pad bi ? bidirectional i/o pad st ? schmitt trigger input pad hcd ? open drain high current drive output pad GM82C765b 6 2. electrical specifications. 2.1 absolute maximum ratings ? operating temp erature ??????? ... ???????? . 0 c (32 f) to 70 c (158 f) ? storage temperature ??????????????? - 55 c ( - 67 f) to +125 c (257 f) ? voltage on any pin with respect to ground ?????????? . ? 0.3 v to vcc +0.3v ? supply voltage with respect to ground ???????????????? ? . 7.0v 2.2 dc electrical characteristics note: maximum limits indicate where permanent device damage occurs. continous operation at these limits is not intended and should be limited to those conditions specified in the dc operating characteristics dc o perating caracteristics: ) f 32 ( c 0 t a = to ) f 158 ( c 70 ; % 10 v 5 v cc = symbol parameter min max units cc v +5v dc power supply 4.5 5.5 v vil input low voltage - data bus & xtosc 0.8 v vih input high volta ge - data bus & xtosc 2.0 v vilt input low threshold voltage - schmitt trigger 0.8 v viht input high threshold voltage - schmitt trigger 2.0 v vol output low - dbx, irq, dma: lo=12.0ma 0.4 v voh output high - dbx, irq, dma: lo= - 5.0ma 2.8 v volhc output lo w - high current: lo=48ma 0.4 v ilul latch up current low 40.0 ma iluh latch up current high - 40.0 ma illx leakage current low 20.0 ma ilhx leakage current high - 20.0 ma icc supply current - 100ua source loads 45.0 ma icchl supply current - 5ma sourc e loads 95.0 ma pd power dissipation - icc max* 425.0 ma pdhl power dissipation - icchl max* 575.0 ma vpqr power qualified reset threshold 2.8 4.35 v note:*:includes open drain high current drives at vol=0.4v GM82C765b 7 2.3 ac timing specifications ) f 32 ( c 0 ta = to ) f 158 ( c 70 : % 10 v 5 vcc + = : pf 100 cl = symbol parameter min max units cy t clock period 60 ns ph t clock active (high or low) 25 ns r t clock rise time (vin 0.8 to 2.0) 5 ns f t clock fall time (vin 2.0 to 0.8) 5 ns ar t a0, cs , dack set up time to rd low 0 ns ra t a0, cs , dack hold time from rd high 0 ns rr t rd width 90 ns rd t data access time from rd low 90 ns df t db to float delay from rd high 10 65 ns aw t a0, cs , dack , ldcr , ldor , set up time to wr low 0 ns wa t a0, cs , dack , ldcr , ldor , hold time from wr high 0 ns ww t wr width 60 ns dw t data set up time to wr high 80 ns wd t data hold time from wr high 0 ns ri t irq reset delay time from rd high 0 1mcy + 150ns wi t irq reset delay time from wr high 0 1mcy + 150ns mcy t dma cycle time 52 mcy am t dma reset delay time from dack low 140 ns ma t dack delay time from dma high 0 ns aa t dack width 90 ns tc t tc width 60 ns rst t reset width - ttl driven clk1 250 ns srst t reset width - software reset 5 mcy rdd t rdd active time low 40 ns wdd t wd write data width low 1/2 (typ) mcy dst t dirc hold & set up to step low 4 mcy stu t dsx hold time from step low 20 mcy stp t step active time low 24 mcy sc t step cycle time 132 mcy (continued on nex t page) GM82C765b 8 symbol parameter min max units idx t idx index pulse width 2 mcy std t dirc hold time after step 96 mcy mr t rd delay from dma 0 ns mw t wr delay from dma 0 ns mrw t rd or wr response from dma high 48 mcy ca t chip access delay from r st low - ttl 32 mcy cas t chip access delay from srst t low 40 mcy xca t chip access delay from rst - osc xt1 at 16mhz 500 us xts t xt2 access delay after rst 9.6mhz 1000 us tcr t tc delay from last dma or irq, rd 0 192 mcy tcw t tc delay from last dma or irq, wr 0 384 mcy note: cy specifies clk1 or xt1 period mcy specifies mclk period, dependent on selec ted data rate wcy specifies wclk period, dependent on selected data rate 2.4 ac timing diagrams (1) read timing . dack , cs , a0 rd data irq ar t rr t ra t rd t df t ri t data valid GM82C765b 9 (2) write timing (3) terminal count (tc) counting (4) dma timing dack , cs ,a0 wr data irq data valid taw tww twa twd twi tdw dma or irq tc tcr tcw ttc tmcy tma tam taa tmrw tmr tmw trd tdw tdf twd data valid dma dack data rd or wr GM82C765b 10 (5) reset timing (6) disk drive select timing (7) clock timing r eset cs trst tca dirc step dsx rdd wd idx tdst tstd tsc tstp tstu tidx trdd twdd clock tr tf tph tph tcy GM82C765b 11 3. architecture the GM82C765b floppy disk subsystem controller is a cmos lsi device that provides all the needed functionality between the host u - processor peripheral bus an d the cable connec - tor to the floppy disk drive. this chip in - tegrates; formatter/controller data separation, write precompensation, data rate seletion, clock generation, drive interface drivers and receivers. host interface the host interface is the host microprocessor peripheral bus. this bus is composed of eight control signals and eight data signals. in the special or pc at modes, irq and dma request are tri - stated and qualified enable, internally provided by the operations register. the data bus, dma, and irq outputs are designed to handle 20 ls - ttl loading. fig 1. GM82C765b internal block diagram control register master status reg data register operation register clock and timing generator disk interface control register host interface ms timer crystal osc 2 digital data separator alu ram 24 8 instruc tion decode rom 1k ? 16 program counter flag logic sate machine data encoder decoder crc generator write precompensation 8 bit data bus drv tc dma irq a0 clk1 clk2 sclk mclk wd pcval plcc version of GM82C765b only 8 bit internal data bus 01 02 wclk rd wr cs dack ldcr ldor hs hdl step dirc rwc 4 1 ds - troo idx wp * dchg rdd we GM82C765b 12 fig 2. typical gm 82c765b application system inputs , except the data bus, are schmi tt trig - ger receivers and can be hooked up to a bus or backplane without any additional buffering. during the command or result phases, the main status register must be ready by the processor before each byte of information is written into or read from the data register. after each byte of data is read from or written into the data register, the cpu should wait for 12us before reading the main status register. bits d6 and d7 in the main status register must be in a 0 and 1 state, respectively, before each b yte of the command word may be written into the GM82C765b. many of the command require multiple bytes. as a result, the main status register must be read prior to each byte transfer to the GM82C765b. during the result phase, bits d6 and d7 in the main sta tus register must both be 1 ? s (d6 - 1 and d7 - 1) before reading each byte from the data register. note that this regarding of the main status register before each byte transfer to the GM82C765b is re - quired only in the command and result phases, and not durin g the execution phase. note also that db6 and db7 in the msr can be polled in - stead of waiting 12us. when they have the right bit settings, the GM82C765b is ready for com - mands. this might save some time. during the execution phase, the main status registe r need not be read. if the GM82C765b is in the non - dma mode, then the receipt of each data byte is indicated by an interrupt signal on pin 16 (irq - 1). the generation of a read signal (rd - 0) will clear the interrupt as well as main microprocesso r interface bus address recode ckt clock ckts GM82C765b floppy disk drive interface connector 40 vcc cc v =+5v 1 rd 2. wr 4 a0 16 irq 19 rst 7 - 14 db0 - db7 15 dma 5 dack 6 tc 3 cs 17 ldor 18 ldcr 24 pcval 23 clk1 21 clk2 22 drv vss 31 * dchg 40 idx 39 troo 36 wp 37 rdd 20 wd 27 we 26 step 29 dirc 28 hdl 35 hs 25 1 ds 30 2 ds 32 gnd gnd vcc vcc 150 w 150 w 150 w 150 w 150 w 1 mo 3 ds 33 2 mo 4 ds 34 rpm rwc 36 * plcc version of GM82C765b GM82C765b 13 output the data onto the dat a bus. if the processor can not handle interrupt fast enough (every 13us for the mfm mode and 27us for the fm mode), then it may poll the main status register and bit d7 (rqm) functions as the interrupt signal. if a write command is in process then the wr signal performs the reset to the interrupt signal. all timings mentioned above double for mini floppy data rates. note that in the non - dma mode it is necessary to examine the main status register to determine the cause of the interrupt signs is could be a data interrupt or a command terminaton interrupt, either normal or abnormal. if the GM82C765b is in the dma mode, no inter - rupt signals are generated during the execution phase. this signifies the beginning of the result phase. when the first byte of data is read during the result phase, the interrupt is auto - matically cleared (irq=0). it should be noted that in pc at usage, non - dma host transfers and not the normal procedure. if the user chooses to do so, the GM82C765b will successfully complete commands, but will always give abnormal termination error status since tc is qualified by an inactive dack . the rd or wr signals should be asserted while dack is true. the cs signal is used in conjunction with rd and wr as a gating function during programmed i/o operations. if the non - dam mode is chosen, the dack signal should be pulled up to cc v . it is important to note that during the result phase all bytes shown in the command table must be read. the read data command for example, has several bytes of data in the result phase. all seven bytes must be read data command. the GM82C765b wil l not accept a new command until all seven bytes have been read. other commands may require fewer bytes to be read during the result phase. the GM82C765b contains five status registers. the main status registers (st0, st1, st2, and st3) are available only during the result phase and may be read only after completing a command. the particular command that has been executed determines how many of the status registers will be read. the byte of data which are sent to the gm82765b to form the command phase, and are read out of the GM82C765b in the result phase, must occur in the order shown in the command table. the command code must be sent first and the other bytes sent in the prescribed sequence. no foreshortening of the command or result phase is allowed. aft er the last byte of data in the command phase is sent to the gm83c765b, the execution phase of automatically starts. in a similar fashion, when the last byte of data is read out in the result phase, the command is automatically ended and the GM82C765b is r eady for a new command. control register the control register provides support logic that latches the two lsbs of the data bus upon receiving ldcr and wr . cs should not be active when this happ ens. these bits are used to select the desired data rate, which in turn controls the internal clock generation. clock switchover is internally ? deglitched ? allowing continuous operation after change data rates. if the control register is not used, the data rate is governed by the supplied clock or crystal. the frequency must be 64x the desired mfm data rate, up to a maximum frequency of 16 mhz. this implies a maximum data rate of 250 kb/s. unless the control register is used. switching this clock must be ? g litchless ? or the device will need to be reset. table 1 presents the control register. GM82C765b 14 table 1. control register cr1 cr0 drv data rate comments rpm (in pc at mode) 0 0 x 500k mfm 1 0 0 x 250k fm 1 0 1 0 250k mfm 0 0 1 1 300k mfm 0 1 0 x 250k mfm, rs t default 1 1 0 x 125k fm, rst default 1 1 1 x 125k 0 master status register the master status register is an eight - bit register that contains the status information of the fdc, any may be accessed at any time. only the master status register may be read and used to facilitate the transfer of data between the processor and GM82C765b. the dio and rqm bits in the master status register indicate when data is ready and in which direction data will be transferred on the data bus. the maximum time between the last rd or wr during a command or result phase and dio and rqm getting set is 12us if 500 kb/s mfm data rate is selected. (if 250 kb/s mfm is selected, the delay is 24us.) for this reason, everytime the master status register is read, the cpu should 12us. the maximum time from the trailing edge of the last rd in the result phase to when db4 (fdc busy) goes low is 12 us. table 2. master status register bits bit no. name symbol description db0 fdd 0 busy d0b fdd number 0 is in the seek mode. if any of the bits is set, fdc will not accept read or write commands. db1 fdd 1 busy d1b fdd number 1 is in the seek mode. if any of the bits is set, fdc will not accept read or write commands. db2 fdd 2 busy d2b fdd number 2 is in the seek mode. if any of the bits is set, fdc will not accept read or write commands. db3 fdd 3 busy d3b fdd number 3 is in the seek mode. if any of the bits is set, fdc will not accept read or write commands. db4 fdc busy cb a read or read command is in progress. fdc will not accept any other commands. db5 execution mode exm this bit is set only during execution phase in non - dma mode. when dbs goes low execution phase has ended and results phase has started. it oper ates only during non - dma mode of operation. db6 data input di0 indicates direction of data transfer between fdc and data register. if dio=1, then transfer is from data register to the processor. if dio=0, transfer is from processor to the data register. db7 request for master rqm indicates data register is ready to send or receive data to or from the process. both bits dio and rqm should be used to perform the handshaking function of ? ready ? and ? direction ? to the processor. GM82C765b 15 table 3. status register 0 bits bit no name symbol description d7 interrupt code ic d7 = 0 and d6 = 0, normal termination of command was completed properly executed. d7 = 0 and d6 = 1, abnormal termination of command (at). execution of command was started but was not successful ly completed. d6 d7 = 1 and d6 = 0. invalid comand issue, (ic). command which was issued was never started. d5 seek end se when fdc completes the seek comand, this flag is set to 1 (high) #d4 equipment check ec if the track 0, signal fails to occur af ter 255 step pulses (recalibrate command). then this flag is set. #d3 not ready nr since drive ready is always persumed true. this will always be a logic 0. d2 head select hs this flag is used to indicate the state of head at interrupt d1 unit select 1 us1 this flag is used to indicate a drive unit number at interrupt d0 unit select 0 us0 this flag is used to indicate a drive unit number at interrupt table 4. status register 1 bits bit no name symbol description d7 end of cyclinder en when the fdc t ries to access a sector beyond the final sector of a cylinder,this flag is set. d6 not used. this bit is always 0 (low) d5 data error de when the fdc detects a * crc error in either the id field or a cylinder, this flag is set. d4 overrun or if the fd c is not serviced by the host system during data transfers within a certain time interval, this flag is set. d3 not data not used. this bit is always 0 (low) d2 no data nd during execution of read data, write deleted data, or scan command, if the fdc ca nnot find the sector specified in the * * idr register, this flag is set. during execution of the read id command, if the fdc cannot read the id field without an error, then this flag is set. during execution of the read a track command, if the starting se ctor cannot be found, then this flag is set. d1 not writeable nw during execution of write data, write deleted data or rormat a track commands. if the fdc detects a wp signal from the fdc, then this flag is set. GM82C765b 16 table 4. status register 1 bits bit no name symbol description d0 missing address mark ma if the fdc cannot detect the id address mark after encountering the index hole twice, then this flag is set. if the fdc cannot detect the data address mark or deleted data address mark, this flag is set. at the same time the md (missing address mark in data field) of status register 2 is set. table 5. status register 2 bits bit no name symbol description d7 not used. this bit is always 0 (low) d6 control mark cm during executing of the read dat a or scan command, if the fdc encounters a sector which contains a deleted data address mark, this flag is set. d5 data error dd if the fdc detects a crc error in the data field, then this flag is set. d4 wrong cylinder wc this bit is related to the nd b it, and when the contents of * * * c on the medium is different from that stored in the idr, this flag is set. d3 scan equal sh during execution of the scan command, if the condition of ? equal ? is satisfied this flag is set. d2 scan not sn during executi on of the scan command, if the fdc cannot find a sector on the cylinder which meets the condition, then this flag is set. d1 bad cylinder bc this bit is related to the nd bit, and when the contents of c on the medium is different from that stored in the i dr, and the contents of c is ff, then this flag is set. d0 missing addres mark in data field md when data is read from the medium, if the fdc cannot find a data address mark or deleted data address mark, then this flag is set. table 6. status register 3 bits bit no name symbol description #d7 not used. will always be logic 0. d6 write protected wp this bit is used to indicate the status of the write protected signal from the fdd #d5 ready ry this bit will always be a logic 1. drive is presumed to be ready. d4 track 0 to this bit is used to indicate the status of the track 0 signal from the fdd. #d3 write protected wp this bit is used to indicate the status of the write protected signal from the fdd d2 head select hs this bit is used to indicate the status of the side select signal to the fdd d1 unit select 1 cylinder us1 this bit is used to indicate the status of the unit select 1 signal to the fdd d0 unit select 2 us0 this bit is used to indicate the status of the unit select 0 signal to the fdd note : * crc - cyclic redundancy check * * idr - internal da ta register * * * c - cylinder # - different from nec765 GM82C765b 17 * data register the eight - bit data register stores data, comma - nds, parameters, and fdd status information. data bytes are read out of, or written into, the dat a register in order to program or obtain the results after a particular command. the relationship between the master status register and the data register status register and the data register and the signals rd , wr , and a0 are shown in table 7. table 7. master status and data registers relationships a0 rd wr function 0 0 0 1 1 1 0 1 0 0 0 1 1 0 0 0 1 0 read main status register illegal illegal illegal read from data re gister write into data register * operations register the operations register provides support logic that latches the data bus upon receiving ldor ad wr . cs should not be active when this happens. the operations register replaces the typical latched port found in floppy subsystems used to control disk drive spindle motors and to select the desired disk drive. table 8 represents the operations register . table 8. operations register or0 or1 or2 or3 or4 or5 or 6 or7 dsel (x) srst dmaen moen1 moen2 (x) (msel) : drive select, if low and moen1 = 1, then 1 ds is active. if high and moen2 = 1, then 2 ds is active, but only in the pc at mode : in GM82C765b this mist be logic 0 for 1 ds and 2 ds to become active. no defined function in GM82C765b. : soft reset, active low. : dma enable, active in special and pc at modes, qualifies dma and irq outputs and dack input. : motor on enable, inverted output 1 mo is active only in pc at : motor on enable, inverted output 2 mo is active in pc at : has no defined function. a spare. : mode select, during a soft reset conditio n, may be used to select between special mode (1) and pc at mode (0). GM82C765b 18 * base, special, and pc at modes base, special, and pc at modes allow subtle differences which the user may find desirable. the control register may be used in any mode without alte ring functionality. * base mode after a hardware reset, rst active, the GM82C765b will be held on soft reset, srst active, with the normally driven signals, dma request and irq request outputs tristated. base mode may be initiated at thi s time by a chip access by the host. although this may be any read or write, it is strongly recommended that the base mode user ? s first chip access be a read of the master status register. once base mode is entered, the soft reset is released, and irq and dma are driven. base mode prohibits the use of the operations register, hence there can be no qualifying by dmaen and no soft resets. the drive select outputs, 1 ds to 4 ds , offer a 1 of 4 decoding of the unit select b its resident in the command structure. pin rwc represents reduce write current and is indicative of when write precompensation is necessary. * special mode special mode allows use of the operations register for the dmaen signal as a qu alifier and to do a software driven device reset, srst . to enter special mode, the operations register is loaded with (1x00x0xx), setting mode select to a logic 1 disabling moen1 and moen2 and causing srst to be active . then a read of the control register address, ldcr and rd , will set the device into special mode. the 1 ds through 4 ds is again offered in this mode, as is rwc . * pc at mode for pc at compatibility, users will write to the operations register, ldor and wr ; this action, performed after a hardware reset, or in the base mode, initiates pc at mode. pc at mode can also be en tered from special mode by loading the operations mode select to a logic 0, disabling moen1 and moen2, and causing srst to be active. then a read of the control register address sets the device into pc at mode. the ds outputs are now replaced with the dsel and moen signals buffered from the operations register. dmaen and srst are supported and compatible with the current bios. rwc pinfunction is now rpm so tha t users with two speed drives may reduce spindle speed per minute to 300 revolutions per minute when active low, used to reduce write current when a slower data rate is selected for a given drive. figure 3 illustrates the relationship among the three modes . GM82C765b 19 fig. 3 flow diagram depicting relationship of base, special, and pc at modes. l polling routine after any reset the GM82C765b, (a hard rst or soft srst , will automatically go into a polling routine. in between c ommands (and between step pulse in the seek command), the GM82C765b polls all four fdds looking for a change in the ready line from any of the drives. since the drive is always presumed ready, an interrupt will only be generated following a reset. this occ urs because a reset forces not ready status, which then promptly becomes ready. note that in special or pc at mode if dmaen is not valid prior to 1ms after reset goes inactive, then irq may be already set and pending when finally enabled onto the bus. the polling of the ready line by the GM82C765b occurs continuously between commands. each drive is polled every 1,024ms, except during the read/write commands . for minifloppies, the polling rate is 2,048ms. the drive polling sequence is 1 - 2 - 4 - 3. please note t hat in the pc at mode, the user will not see the polling at the drive select signals, figure 4 illustrates the drive select polling time fig. 4. drive select polling timing * devece resets the GM82C765b supports both hardware reset (rst) pin (19) and a software reset ( srst ) through use of the operations register. the rst pin will cause a device reset for the active duration. rst causes a default to base mode, and default selects 250k mfm (or 125k fm, code dependent) as the data rate (16 mhz input clock). srst will reset the microcontroller as did the rst, but will not affect the value set for the internal timers - hut, ftl, and srt. if the xtal oscillators are used, instead of the ttl driven clock inputs, the hard ware rst active time requirement will bootstrap the circuit into guaranteed oscillation in a fixed amount of time. the extended reset time allows the growth of the oscillation to produce stable internal clock timing write 80 to oper reg special mode read cont reg ldcr, rd write 00 to oper reg read master status reg. write to oper reg. pc at mode hardware reset base mode read cont reg. ldcr, rd ds1 ds2 ds3 ds4 GM82C765b 20 * data separator the data separator is a digital phase lock loop floppy disk data separator (dpll). it was designed to address high performance error rates on floppy disk drives, and to provide superior performance in terms of available bit jitter tolerance. it contains the necessary logic to achieve classical 2nd order, type 2, phase locked loop performance. dpll is used as the data separator in the GM82C765b system. figure 5 illustrates the dpll implified block diagram. the bit jitter tolerance for the data separator is 60%, which guarantees an error rate of < 10e - 9. * write precompensation the bm82c765b maintains the stand first level algorithm to determine when write precompensation should be applied. the early and late signals are used internally to select the appropriate delay in the wr ite data pulse stream. the encoded write data signal is synchronized to the 16 mhz clock if this is the frequency on clk1 pin (23), and clocked through a shift register before a multiplexer gates the chosen bit to the output. the output data pulse width has a 25% duty cycle, i.e., one fourth of the bit cell period, and equal to one half the wclk period. when pcval pin (24) = 1, all data will be precompensated by + 187ns precompensation will be generated. for frequencies other than 16 mhz on the clk1 pin , the precompensation values will be two and three clock cycles respectively. when the non - standard data rate using clk2 is chosen, the mfm precompensation will always be two clock cycles. for 9.6mhz, this is +208ns. in this case, this pcval function is d isabled fig. 5. dpll simplified block diagram cd2 cd1 data synchronization rdata resynchronizatio n digital controlled oscillator transient r esponse state filtering steady state frequency filtering summer p h a s e dete - ction clock generation sclk refclk sepd sepclk phase sepclk dskd GM82C765b 21 * clock generation this logical block provides all the clocks needed by the GM82C765b. they are: sampling clock (sclk), write clock (wclk), and the master clock (mclk). sclk driv es the dpll data separator used during data recovery. this clocks ? s frequency is always 32 times the selected data rate. wclk is used by the encoder logic to place mfm or fm on the serial wd - stream to the disk. wclk always has a frequency two times the sel ected data rate. mclk is used by the microsequencer. mclk and mclk clock all latches in a two - phase scheme. one microinstruction cycle is four mclk cycles. mclk has a frequency times the fm data rate. table 9 presents the clock data rate. figure 6 illust rates the xtal oscillator circuits for the 44 - pin plcc configuration. table 9. clock data rate data rate code slck mclk wclk 500kbit/s mfm 16.0mhz 4.0mhz 1.0mhz 250kbit/s fm 8.0mhz 4.0mhz 500.0mhz 250kbit/s mfm 8.0mhz 2.0mhz 500.0mhz 125kbit/s fm 4.0m hz 2.0mhz 250.0mhz 300kbit/s mfm 9.6mhz 2.4mhz 600.0mhz fig 6. xtal oscillator circuits for the 44 pin plcc c 2 c 4 c 1 xt1 c 3 23 22 25 26 xt1 xt2 xt2 9.6mhz + 100 ppm r series = 30 ohm max c shunt = 10 pf max c1 = 68 pf 5% mica c2 = 56 pf 5% mica series resonant xt2 9.6m hz + 100 ppm r series = 30 ohm max c shunt = 10 pf max c3 = 47 pf 5% mica c4 = 15 pf 5% mica series resonant GM82C765b 22 * command parameters the GM82C765b is capable of performing 15 different commands. each com mand is initiated by a multibyte transfer from the processor. the results after execution of the command may also be a multibyte transfer back to the processor. the commands consist of three phases : command phase, execution phase, and the result phase. c ommand phase - the floppy disk controller (fdc) receives all information required to perform a particular operation from the processor. execution phase - the fdc performs the operation it was in structed to do. result phase - after completion of the opera tion, status and other housekeeping in formation are made available to the processor table 10. GM82C765b commands read data read deleted data write data write deleted data read a track read id format a track scan equal scan low or equal scan high or e qual table 10. lists the 15 GM82C765b commands. table 11. through 25 are presented to show the required parameters and results for each command. most commands require nine command bytes during the result phase. the ? w ? to the left of each byte indicates a command phase byte to be written. an ? r ? indicates a result byte. table 11. read data phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x sk x 0 x 0 x 1 hs 1 us1 0 us0 command codes command w w w w w w w c h r n eot gpl dtl sector id information prior to command execution. the four bytes are compared against header on floppy disk. execution data transfer between fdd and main system results r r r r r r r sto st1 st2 c h r n status information after command execution. se ctor id information after command execution. GM82C765b 23 table 12. read deleted data r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x sk x 0 x 1 x 1 hs 0 us1 0 us0 command codes command w w w w w w w c h r n eot gpl dtl sector id information prior to command execution. the four bytes are compared against header on floppy disk. execution data transfer between fdd and main system results r r r r r r r sto st1 st2 c h r n status information after command execution. sector id information after command execution. table 13. write data phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x 0 x 0 x 0 x 1 hs 0 us1 1 us0 command codes command w w w w w w w c h r n eot gpl dtl sector id information prior to command execution. the fo ur bytes are compared against header on floppy disk. execution data transfer between fdd and main system results r r r r r r r sto st1 st2 c h r n status information after command execution. sector id information after command execution. GM82C765b 24 table 14. write deleted data phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x 0 x 0 x 1 x 0 hs 0 us1 1 us0 command codes command w w w w w w w c h r n eot gpl dtl sector id information prior to command execution. the four bytes are compared against header on floppy disk. execution data transfer between fdd and main system results r r r r r r r sto st1 st2 c h r n status information after command execution. sector id information after command execution. table 15 . read a track phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w 0 x mf x sk x 0 x 0 x 0 hs 1 us1 0 us0 command codes command w w w w w w w c h r n eot gpl dtl sector id information prior to command execution. execution data transfer between fdd and main system . fdd reads all data fields from index hole to eot results r r r r r r r sto st1 st2 c h r n status information after command execution. sector id information after command execution. GM82C765b 25 table 16. read id phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks command w w 0 x mf x 0 x 0 x 1 x 0 hs 1 us1 0 us0 command codes execution the first correct id information on the cylinder is stored in data register. results r r r r r r r sto st1 st2 c h r n status information after c ommand execution. sector id information after command execution. table 17. format a track phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w 0 x mf x 0 x 0 x 1 x 1 hs 0 us1 1 us0 command codes command w w w w n sc gpl d bytes / sector sector/tra ck gap 3 filler byte execution floppy disk controller (fdc) formats an entire track. results r r r r r r r sto st1 st2 c h r n status information after command execution. in this case, id information has no meaning. GM82C765b 26 table 18. scan e qual phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x sk x 1 x 0 x 0 hs 0 us1 1 us0 command codes command w w w w w w w c h r n eot gpl stp sector id information prior to command execution. execution data transfer between fdd and m ain system results r r r r r r r sto st1 st2 c h r n status information after command execution. sector id information after command execution. table 19. scan low or equal phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x sk x 1 x 1 x 0 hs 0 us1 1 us0 command codes command w w w w w w w c h r n eot gpl stp sector id information prior to ommand execution. execution data transfer between fdd and main system results r r r r r r r sto st1 st2 c h r n status information afte r command execution. sector id information after command execution. GM82C765b 27 table 20. scan high or equal phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks w w mt x mf x sk x 1 x 1 x 1 hs 0 us1 1 us0 command codes command w w w w w w w c h r n eot gpl stp sector id information prior to command execution. execution data transfer between fdd and main system results r r r r r r r sto st1 st2 c h r n status information after command execution. sector id information after command execution. tabl e 21. recalibarte * phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks command w w 0 x 0 x 0 x 0 x 0 x 1 hs 1 us1 1 us0 command codes execution head retracted to track zero table 22. sense intrrupt status phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks command w 0 0 0 0 0 1 1 1 command codes results r status information about the fdc at the end of seak operation table 23. specify phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks 0 0 0 0 0 0 1 1 command w w srt hut hlt command codes execution head retracted to track zero n d GM82C765b 28 table 24. sense drive status phase r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks command w w 0 x 0 x 0 x 0 x 0 x 0 hs 0 us1 0 us0 command codes execution st3 status information about the fdc table 25. seek r/w d7 d6 d5 d4 d3 d2 d2 d0 remarks 0 x 0 x 0 x 0 x 1 x 1 hs 1 us1 1 us0 command w w w ncn command codes execut ion head is positioned over proper cylinder on the diskette. table 26 defines, in alphabetical order, the symbols used in command tables 11 through 25. table 26. command symbol descriptions symbol name description a0 address line 0 a0 controls selec tion of main status register (a0 = 0) or data register (a0 =1) c cylinder number c stands for the current/selected cylinder (track) numbers 0 through 255 of the medium. d data d stands for the data pattern which is going to be written into a sector. d7 - d0 data bus 8 - bit data bus, where d7 stands for a most significant bit, and d) stands for a least significant bit. dtl data length when n is defined as 00, dtl stands for the data length which users are going to read out or write into the sector. eof end of track eot stands for the final sector number on a cylinder. during read or write operations. fdc will stop data transfer after a sector number equal to eot. gpl gap length gpl stands for the length of gap 3. during the format command. it determines th e size of gap 3. h head address h stands for head number 0 or 1, as specified in the id field. hlt head load time hlt stands for the head load time in fdd (2 to 254ms in 2ms increments) hs head select hs stands for a selected head number 0 or 1 and cont rols the polarity of pin 25 (in 40 pin dip) or pin 28 (in 44 pin plcc) hut head unload time hut stands for the head unload time after a read or write operation has occurred (16 to 240ms in 16ms increments). mf fm or mfm if mf is low, fm mode is selected . if it is high, mfm mode is selected. mt multitrack if mt is high, a multitrack operation is performed. if mt =1 after finishing read / write operation on side 0, fdc will automatically start searching for sector 1 on side 1 GM82C765b 29 symbol name descri ption n number n stands for the number of data bytes written in a sector. ncn newcylinder number ncn stands for a new cylinder number which is going to be reached as a result of the seek operation. desired position of head. nd non - dma mode nd stands f or operat i on in the non - dma mode. pcn present cylinder pcn stands for the cylinder number at the completion of the sense interrupt status command position of head at present time.. r record r stands for the sector number which will be read or written. r/w read/write r/w stands for either read or write signal. sc sector sc indicates the number of sectors per cylinder. sk skip sk stands for skip deleted data address mark. srt step rate time str stands for the stepping rate for the fdd (1 to 16ms in 1ms increments). stepping rate applies to all drives. in 2 ? s complement format, f(hes) = 1ms, e(hex) =2ms, etc st0 st1 st2 status 0 status 1 status 2 sto = 3 stands for one of four registers which store the status information after a command has been executed. this information is available during the result phase after command execution. st3 status 3 these registers should not be confused with the main status register (selected by a0 = 0). st0=3 may be read only after 3 command has been executed and co ntains information relevant to that particular command. stp during a scan operation, if stp=1, the data in contiguous sectors is compared byte by byte with data sent from the processor (or dma); if stp=2, then alternate sectors are read and compared. u s0, us1 unit select us stands for a selected drive; binary encoded, 1 of 4. command descriptions read data a set of nine byte words are required to place the fdc into the read data mode. after the read data command has been issued, the fdc loads the hea d (if it is unloaded state), warts the specified head setting time (defined in the specify command begins reading id address marks and id fields. when the current sector number ( ? r ? ) stored in the id register (idr) compares with the sector number read off the diskette, then the fdc outputs data (from the data bit) byte - to - byte to the main system via the data bus. after completion of the read operation from the current sector, the sector number is incremented by one, and the data from the next sector is read and output on the data bus. this continuous read function is called a ? multi - sector read operation. ? the read data command may be terminated by the receipt of a terminal count signal. tc should be issued at the same time that the dack f or the last byte of data is sent. upon receipt of this signal, the fdc stops outputting data to the processor, but will continue to read data from the current sectors, check crc (cyclic redundancy count) bytes, and the end of the sector terminate the read data command. the amount of data which can be handled with a single command to the fec depends upon mt (multi - track), mf(mfm/fm), and n(number of bytes/sector). table 27 lists the transfer capacity. the ? multi - track ? function (mt) allows the fdc to read da ta from both sides of the diskette. for a particular cylinder, data will be transferred starting at sector 1, side 0 and completing at sector l, side 1 (sector l = last sector on the side). note, this function pertains to only one cylinder (the same track ) on each side of the diskette. when n=0, then dtl defines the data length which the fdc must treat as a sector. if dtl is smaller than the actual data length in a sector, the GM82C765b 30 data beyond dtl in the sector is not sent to the data bus. the fdc reads (inte rnally) the complete sector performing the crc check, and depending upon the manner of command termination, may perform a multi - sector read operation. when n is non - zero, then dtl has no meaning and should be set to ff hexadecimal. table 27. transfer cap acity multi - track mt mfm/fm mf bytes/ sector n maximum transfer capacity (number of sectors) final sector read from diskettes 0 0 0 1 00 01 (128) (26) ? 3.328 (256) (26) ? 6.656 26 at side 0 or 26 at side 1 1 1 0 1 00 01 (128) (52) ? 6.658 (256) (52) ? 13.312 26 at side1 0 0 0 1 01 02 (256) (15) ? 3.840 (512) (15) ? 7.680 15 at side 0 or 15 at side 1 1 1 0 1 01 02 (256) (30) ? 7.680 (512) (30) ? 15,360 15 at side 1 0 0 0 1 02 03 (512) (8) ? 4.096 (1024) (8) ? 8.192 8 at side 0 or 8 at side 1 1 1 0 1 02 03 (512) (16) ? 8.192 (1024) (16) ? 16.384 8 at side 1 at the completion of the real data command, the head is not unloaded until after head unload time interval (specified in the specify command) has elapsed. if the processor issues another comman d before the head unloads, then the head setting time may be saved between subsequent reads. this time out is particularly valuable when a diskette is copied from one drive to another. if the fdc detects the index hole twice without finding the right sect or, (indicated in ? r ? ), then the fdc sets the nd (no data) flag in status register 1to a 1 (high), and terminates the read data command (status register 0 also has bits 7 and 6 set to 0 and 1 respectively.) after reading the id and data fields in each s ector, the fdc checks the crc bytes if a read error is detected (incorrect crc in id field), the fdc sets the de(data error) flag in status register 1 to 1 (high) if a crc error occurs in the data field, the fdc also sets the dd(data error in data field) f lag in status register 2 to 1(high) and terminates the read data command. (status register 0 also has bits 7 and 6 set to 0 and 1 respectively.) if the fdc reads a deleted data address mark off the diskette, and the sk bit (bit d5 in the first command wo rd) is not set (sk =0), then the fdc sets the cm(control mark) flag in status register 2 to a 1 (high), and terminates the read data command, after reading all the data in the sector. if sk = 1, the fdc skips the sector with the deleted data address mark a nd reads the next sector. the crc bits in the deleted data field are not checked when sk = 1. during disk data transfers between the fdc and the processor, via the data bus, the fdc must be serviced by the processor every 27 us in the fm mode, land every 13 us in the mfm mode, or the fdc sets the or (overrun) flag in status register. 1 to a 1 (high), and terminates the read data command. table 28. c, h, r, and values id information at resul t phase mt hd final sector transferred to processor c h r n 0 less then eot nc nc r+1 nc 0 equal to eot c+ 1 nc r=01 nc 1 less then eot nc nc r+1 nc 0 1 equal to eot c+1 nc r=01 nc 0 less then eot nc nc r+1 nc 0 equal to eot nc lsb r=01 nc 1 less then eot nc nc r+1 nc 1 1 equal to eot c+1 lsb r= 01 nc notes : nc (no change) : the same value the one at the beginning of command execution. lsb (least significant bit): the least significant bit of h is complemented. GM82C765b 31 write data a set of nine bytes is required to set the into dc the write data mode, after the commawrite data and has been issued the fdc loads the head (if is in the unloaded state), waits the specified head settling time (defined in the specify command), and beings reading id fields, when all four bytes loaded during the command (c,h,r ,n) match the four byte of id field from the processor byte - by - byte via the data bus and outputs it to the fdd. after writing data into the current sector, the sector number stored in ? rr ? is incremented by one, and the next data field is written into. the fdc continues this multisector write operation ? until the issuance of terminal count signal. if a terminal count signal is sent to the fdc it continues writing into the current sec tor to complete the data field. if the t erminal count signal is received w hile a data field is being written remainder of the data field is filled zeros. the fdc reads the id field of each sector and checks the crc bytes. if the fdc detects a read error (crc error) in one of the id fields, it sets the de (data error) flag of sta tus register 1 to a 1 (high) and terminates the write data command. (status register 0 also has bit 7 and 6 set to 0 and 1 respectively.) the write command operates in much the same manner as the read command. the following items are the same., and one s hould refer to the read data command for details. the write command operates in much the same manner as the read command. the following items are the same, and one should refer to following items are the same, and one the read data command for details: transfer capacity en (end of cylinder) flag nd (no data) flag head unload time interval id information when the processor terminates command definition of dtl when n=0 and when n=0 in the write data mode, data transfers between the processor and fdc via the data bus, must occur every 27 us in the fm mode and every 13 us in the mfm mode. if the time interval between data transfers is longer than this, then the fdc sets the or (overrun) flag in status register 1 to a 1 (high) and terminal the write data address mark. write deleted data this command is the same as the write data command except a deleted data address mark is written at the beginning of the data field instead of the normal data address mark. read deleted data this command is the same as the read data command except that when the fdc detects a data address mark at the beginning of a data field (and sk = 0 (low)), it will read all the data in the sector and set the cm flag in status register 2 to a 1 (high), and then terminate the comma nd. if sk = 1, then the fdc skps the sector with the data address mark and reads the next sector. read a track this command is similar to the read data command except that this is a continuous read operation where the entire data field from each of the sec tors is read. immediately of the sectors is read. immediately after sensing the index hole. the fdc starts reading all data fields on the track as continuous biocks of data. if the fdc finds an error in the id or data crc check bytes, it continues to. this command terminates when the number of sectors read is equal to eot. if the fdc does not find an id address mark on the diskette after it senses index hole for the second time, it sets the ma (missing address mark) flag in status register 1 to a 1 (high) a nd terminates the command. (status register 0 has bits 7 and 6 set to 0 and 1 respectively.) GM82C765b 32 read id the read id command is used to give the present position of the recording head. the fdc stores the values from the first id field it is able to read. if no proper id address mark is found on the diskette before the index hole is encountered for the second time, then the ma (missing address mark) flag in status register 1 is set to a 1 (high), and if no data is found then the nd (no data) flag is also set in status register 1to a 1 to a 1 (high). the command is then terminated with bits 7 and 6 in status register 0 set to 0 and 1 respectively. during this command there is no data transfer between fdc and the cpu except during the result phase. format a trac k the format command allows an entire track to be formatted . after the index hold is detected, data is written on the diskette; gaps , address marks, id fields and data fields, all per the ibm system 34 (double density) or system 3740 (single density ) for mat are recorded. the particular format which will be written is controlled by the values programed into n (number of bytes/sector), sc (secros/cylinder), gpl (gap length), and d (data pattern) which are supplied by the processor during the command phase. the data field for each sector is supplied by the processor; that is four data requests per sector are made by the fdc for c (cylinder number). h (head number), r (sector number) and n (number of bytes/sector). this allows the diskette to be formatted with nonsequential sector numbers, if desired. the processors must send new values for c, h, r, and n to the wd37c65/a/b for each sector on the track. if fdc is set for the dma mode, it will issue four dma interrupts per sector and the processor must supply c, h,r, and n loads for each sector. the contents of the r register are incremented by 1 after each sector is formatted; thus, the r register contains a value of r when it is read during the result phase. this incrementing and formatting continues for the who le track until the fdc deterts the index hole for the second time, where upon it terminates the command. table 29 shows the relationship between n, sc, and gpl for various sector sizes table 29. n, sc and gpl relationship format sector size n sc gpl ? gpl ? 8 ? standard floppy 128 bytes/sector 00 1a 07 1b 256 01 0f 0e 2a 512 02 08 1b 3a 1024 03 04 47 8a 2048 04 02 c8 ff fm mode 4096 05 01 c8 ff 256 01 1a 0e 36 512 02 0f 1b 54 1024 30 08 35 74 4 096 05 02 c3 ff mfm mode 4 8192 06 01 c3 ff 5 4 1 ? minifloppy 128 00 12 07 09 128 00 10 10 19 256 01 08 18 30 512 02 04 46 87 1024 03 02 c8 ff fm mode 2048 04 01 c8 ff 256 01 12 0a 0c 256 01 10 20 32 512 02 08 2a 50 1024 03 04 80 f0 2048 04 04 c8 ff mfm mode 4 4096 05 01 c8 ff 3 2 1 ? sony microfloppy 128 0 0f 07 1b 258 1 09 0e 2a fm mode 512 2 05 1b 3a 256 1 0f 1b 54 512 2 09 1b 54 mfm mode 4 1024 3 05 3 5 74 GM82C765b 33 scan commands the scan commands allow data which is being read from the diskette to be compared against data which is being supplied from the main system. the fdc compares the data on a byte - by - byte basis and looks for a sector of data which me ets the conditions of d fdd=d processor, d fdd GM82C765b 35 table 31. interrupt cause seek end interrupt code cause bit 5 bit 6 bit 7 ready line dhanged state, either polarity 0 1 1 normal termination of seek or recalibrate command 1 0 0 abnormal termination of seek or recalibrate command 1 1 0 abnormal termination of seek or recalibrate command the sense interrupt status command is used in conjunction with the seek and recalibrate comma nds which have no result phase. when the disk drive has reached the desired head position, the GM82C765b will set the interrupt line true. the host cpu must then issue a sense interrupt status command to determine the actual cause of the interrupt, which c ould be seek end or a change in ready status from one of the drives. the specify command sets the initial values for each of the three internal timers. the hut (head unload time) defines the time from the end of the execution phase of one of the read/wri te commands to the head unload state. this timer is programmable from 16 to 240ms in increments of 16ms (01 = 16ms, 02 = 32ms ? of16 = 240ms). the srt (step rate time) defines the time interval between adjacent step pulses. this timer is programmable from 1 to 16ms in increments of 1ms (f = 1ms, e = 2ms, d = 3ms, etc.). the hlt (head load time)defines the time between when the head load signal goes high and the read/write operation starts. this timer is programmable from 2 to 254ms in increments of 2ms (01 = 2ms, 02 = 4ms, 03 = 6ms ? 7f = 254ms). (01 = 2ms. 02 = 4ms, 03 = 6ms ? 7f = 254ms). fig. 7. recalibrate and sense interrupt relationship seek or recalibrate) 0 command command execution sense interrupt status command result int cs a 0 rd wr dio rqm op code for instruction written into gmb2c765b hd/drive not written into gmb2c765b op code for instruction written into gmb2c765b ncn written into gmb2c765b rcn read by pr ocess status register sto read by processor GM82C765b 36 the specify command sets the initial values for each of the three internal timers. the hu t(head unload time) defines the time from the end of the execution phase of one of the read write commands to the head unload state this timer is programmable from 16 to 24oms in increments of 16ms.(01=16ms, 02=32ms ? of16=240ms). the srt (step rate time) defines the time interval between adjacent step pulses. this timer is programmable from 1 to 16ms in increments of 1ms (f=1ms, e=2ms, d=3ms, etc.). the hlt (head load time) defines the time between when the head load signal goes high and the read/write ope ration starts. this timer is programmable from 2 to 254ms in increments of 2ms (01=2ms, 02=4ms, 03=6ms ? 7f=254ms). the time intervals mentioned above are a direct function of the clock (clk on pin 23). times indicated above are for a 16mhz clock; if the cl ock was reduced to 8mhz, then all time intervals are increased by a factor of 2. sense drive satus this command may be used by the processor whenever it wishes to obtain the status of the fdds. status register 3 contains the drive status information st ored internally in dfc registers. if an invalid command is sent to the fdc (a command not defined above), then the fdc will terminate the command after bits 7 and 6 of status register 0 are set to 1 and 0 respectively. no interrupt is generated during this condition. bits 6 and 7 (dio and rqm) in the main status register are both high (1), indicating to the processor that the GM82C765b is in the result phase and the contents of status register 0 (sto) must be read. when the processor reads status register 0 , it will find an 80 hex, indicating an invalid command was received. a sense interrupt status command must be sent after a seek or recalibrate interrupt; otherwise the fdc will consider the next command to be an invalid command. gap4a 40x ff sync 6x 0 0 iam fc gap1 26x ff sync 6x 00 idam fe c y l h d s e c n o c r c gap 11x ff sync 6x 00 data am fb or f8 data1 c r c gap3 gap4b index repeat n times fig 8. GM82C765b fm mode format iam idam data am gap4a 80x ff sync 12x 00 3x c2 fc gap1 50x 4e sync 12x 00 3x a1 fe c y l h d s e c n o c r c gap2 22x 00 sync 12x 00 3x fb a1 f8 data 1 c r c gap3 1 gap4b index repeat n times fig 9. GM82C765b mfm mode format |
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