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PDSP16540 FEBRUARY 1995 ADVANCE INFORMATION
DS3715 - 2.1
PDSP16540
32K BUCKET BUFFER
(Supersedes version in December 1993 Digital Video & Digital Signal Processing IC Handbook, HB3923-1)
The PDSP16540 Bucket Buffer is for use in systems which require a reservoir in which a block of data is accumulated, whilst previous data is being transferred to other system elements and then processed. It thus prevents the loss of incoming data whilst the previous block is being processed. Like a FIFO all address are generated internally. It differs from a normal FIFO, however, by allowing the user to define both the length of the data block and also the amount of the old data to be re-read before the new data is added. The latter feature supports the block overlapping requirements of Digital Signal Processing Systems performing Fast Fourier Transforms. It also provides wide, 32 bit, input and output buses, unlike normal byte wide FIFO's. This wide configuration supports the16 bit real and imaginary components of the complex data found in many DSP systems. In particular, the device can be directly connected to the PDSP16510 FFT Processor without any external logic. The FFT Processor requires the support of an input buffer when 1024 point transforms are to be continuously performed and no incoming data is to remain un-processed. The number of words, which are read as a complete block, can be programmed in multiples of 32 up to a maximum of 1024. The amount of new data in this block can separately be programmed in multiples of 32 words. In this manner the percentage of new data in a complete block is under the control of the user, and the device is not restricted to only supporting the requirements of the PDSP16510. A Read Me Flag is raised at a user defined point during the loading of new data. This allows the next system component to prepare itself to accept data. Data is not actually transferred, however, until all the user defined amount of new data has been loaded, and a Data Available Flag goes active. The gap between the two flags can be programmed to provide sufficient time to prepare the device which is to accept data from the buffer. This provide a much more flexible solution than the simple Full Flag offered by a standard FIFO.
FEATURES
s 1K x 32 bit dual port RAM for use as a reservoir in data flow systems s s s Up to 40 MHz read rates and 16 MHz write rates Buffer size user programmable up to 1k words A user programmble amount of old data can be reread before new data is added s Provides the input buffer requirements for the PDSP16510 FFT Processor when 1024 point continuous transforms are performed s s User programmable get ready to Read Me Flag Data Available Flag indicates the required amount of new data has been acquired s 84 Pin PGA or 132 Pin QFP
WRITE STROBE WRITE ENABLE
READ STROBE
ASSOCIATED PRODUCTS
SYNC LOGIC RESET READ 1K X 32 BIT DUAL PORT RAM WRITE ADDRESS READ ADDRESS 32 BIT O/P DATA READ ME FLAG
PDSP16510 FFT Processor PDSP16520 Quad Port Synchronous RAM PDSP16116 Complex Multiplier PDSP16318 Complex Accumulator PDSP16330 Cartesian to Polar Converter PDSP16340 Polar to Cartesian Converter
MODE CONTROL 32 BIT I/P DATA
WRITE
CONTROL LOGIC DATA AVAIL FLAG
Figure 1. Simplified Block Diagram
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PDSP16540
NAME IP31:0 D31:0 TYPE I/P O/P SIGNAL DESCRIPTION 32 bit input bus. If MD5 is high, pins IP16:31 are redundant 32 bit output bus. This bus will be high impedance until the Data Available Flag is active. It then remains low impedance until the required amount of data has been read. D15:0 become inputs during reset, and may be used to define the operating conditions. RS WS I/P I/P The read strobe must be continuous, and the rising edge transfers data to the output pins. Write strobe used to load data into the internal RAM. This strobe may be asynchronous to the read strobe, and may be continuous or intermittent. WEN DAV I/P O/P Write enable which when low allows the write strobe to load data. Data Available Flag. This signal goes active low when the required amount of new data has been written to the RAM. The complete block of data will then be read from the RAM in sequence using the read strobe. The next system component must be ready to accept the information, which will consist of both new and old data, in amounts defined by MD2:1. The flag will go in-active for one read strobe period every time new data is written to the RAM, and stays in-active when the complete block has been transferred. RMF O/P Read Me Flag. This signal goes active high when a user defined amount of new data has been written to the RAM. It can go active before DAV goes active, and thus allows the system to prepare itself for data when it becomes available. It stays active until the complete block has been read. MD0 I/P When MD0 is low the block length is 1024 words. When it is high the block length is defined in groups of 32 words by the data on D4:0 during reset. MD2:1 MD2:1 define the amount of new data within the block length as defined above. The options are 1024 (00), 512 (01), 256 (10), or the number defined in groups of 32 words by D9:5 during reset (11). When the number of new words is less than the block length defined by MD0, the first words read from the RAM will be data previously stored. MD4:3 I/P MD4:3 define the number of new words which are written before the Read Me Flag goes active. The options are 1024, 512, 256 or the number defined in groups of 16 words by D15:10 during reset. MD5 I/P When this pin is high the device will support the real transform mode of the PDSP16510. Only IP15:0 input pins are then used and 2 blocks are acquired before the flags go active. Both blocks are then read in parallel using the 32 output pins. RES I/P When this pin is low outputs D15:0 become inputs, which are used to define the operating mode if the internal options have not been selected. The input can be power on reset. GND VCC I/P I/P Four ground pins. All must be connected Four +5 volt pins.All must be connected
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PDSP16540
N
D7
D8
D10
D12
D14
VDD
D17
GND
D19
D21
D23
D25
D26
M
D6
D9
D11
D13
D15
D16
D18
D20
D22
D24
D27
L
D4
D5
D28
D29
K
D2
D3
D30
D31
J
D0
D1
MD0
MD1
H
GND
RMF
MD2
GND
G
RS
WEN
MD3
MD4
F
VDD
DAV
MD5
VDD
E
WS
IP 0
IP 31
RES
D
IP 1
IP 2
IP 29
IP 30
C
IP 3
IP 4
IP 27
IP 28
B
IP 5
IP 8
IP 10
IP 12
IP 14
IP 16
IP 17
IP 19
IP 21
IP 23
IP 26
A
IP 6
IP 7
IP 9
IP 11
IP 13
VDD
IP 15
GND
IP 18
IP 20
IP 22
IP 24
IP 25
1
2
3
4
5
6
7
8
9
10
11
12
13
Pin Out Diagram - Bottom View (84pin PGA - AC84)
FUNCTIONAL DESCRIPTION
The PDSP16540 is designed for use in synchronous data flow systems in which the transfer between system elements is contolled by a continuously available system clock. This system clock is usually at the maximum rate that the system elements will allow, since it is governing the rate at which processing can be performed on the acquired data. The rate at which external data is actually inputed to the system ( the sampling rate in DSP terminology ) is usually much slower than the internal system, or computational, rate. The PDSP16540 then provides a reservoir for data which is acquired at the sampling rate and then processed with the higher speed system clock rate. Data is written to the RAM using an asynchronous write strobe when a write enable input is active. The enbling signal must meet the set up and hold times given in Table 1. Data is read from the RAM using a read strobe which is expected to be continuously availble and not to just go active when read operations are actually needed. It is normally the high speed system clock discussed earlier. All RAM addresses are generated internally since the device is partitioning consecu-
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PDSP16540
tive data inputs into pre-defined blocks, which are then transferred to the rest of the system at the system clock rate. All internal read and write operations are actually performed by the continuous read strobe. When a write strobe is received, internal syncronization occurs and the write operation is actually done with the read strobe. If data is being read from the RAM when a write operation is requested, the read sequence will be interupted for one read strobe period. The flag indicating that data is available goes in-active for this strobe period and the next system element should not accept data during this perfiod. The correct operation of the write synchronization circuit requires that write operations occur at a slower rate than that of the read strobe. In fact the write strobe period must be at least twice the read strobe period plus some internal delays. Table 1 gives the actual maximum writing rates, and shows that the rate must be reduced when the block of data which is read from the RAM is not completely composed of new data. The maximum writing rate is limited by the need to have read a complete block before the requested amount of new data has been loaded. A Data Available Flag is provided which goes active when the pre-defined number of words have been written to the RAM. The data read sequence then automatically starts and the flag will go in-actice when the pre-programmed amount of data has been read. An additional get ready to Read Me Flag is provided which can separately be programmed to occur at any point during the block write operation. This flag has no internal action but can be used to warn the next system element that data is to be expected. DEFINING THE LENGTH OF THE BLOCKS The amount of new data written to the RAM before the Data Availble Flag is raised, and the amount of data which is then read from the RAM are separately definable. In this way the user can define the amount of old data which is re-read before the new data will be accessed. These overlapping data blocks are required in systems performing frequency domain transforms, when a window operator is applied to prevent frequency discontinuities between the blocks. The resulting loss of information, caused by de-emphasizing the data near the edges, is recovered by overlapping the blocks. The mode control input MD0 is used to define the block length during the read operation. When MD0 is tied low the read block length will be 1024 words. When MD0 is tied high the block length is defined by the state of pins D4:0, which become inputs whilst the RESET input is active. A tri-state buffer is needed on the outputs which is only enabled during RESET, and whose inputs define the block length. These five inputs allow the block length to be defined in multiples of 32 words, from a minimum of 32 up to the maximum of 1024. The decode of the five bits (0 - 31) should be considered as defining additional blocks of 32 words above the 32 word minimum. The mode control inputs MD2:1 are used to define the number of new words in the total block defined as above. Decodes 0 through 2 define 1024, 512, and 256 new words respectively. Decode 3 is used when a finer definition is needed, and makes use of the states of pins D9:5 during reset. The decodes of the five bits (0 - 31) then define additional groups of 32 words above a 32 word minimum. USING THE FLAGS The data available flag (DAV) always goes active when the required number of new words have been written to the buffer, and the first word to be read is available at the output pins. The rising edges of the read strobes must then be used by the system to transfer the complete block of data to the next system component. The minimum write periods given in Table 1 ensure that the first word will have been read before it is replaced with new data. Internal logic will increment the read address counter and DAV will go in-active when the complete block has been read. The DAV output will also go in-active for one read strobe period every time a new word is written to the buffer. Write operations to the next system component should be inhibited for that cycle, and the DAV ouput must be used as write enable for the next device. All DAV transitions are produced by the rising edge of the read strobe. An additional flag is provided which can be used to warn the next system component that data is to be expected. This get ready to read me flag (RMF) can be programmed to occur at any point (within 16 words) during the write operation. Decodes 0 through 2, from mode control inputs MD4:3, will cause the flag to go active after 1024, 512, or 256 words respectively have been loaded. Decode 3 allows the state of pins D15:10 during RESET to be used to define the transition point. Decodes 0 through 63 define form 0 to 63 additional groups of 16 words after the minimum 16 words have been loaded. The RMF flag goes in-active at the same time DAV goes in-active. The gap between the RMF and DAV outputs should be sufficient to ensure that the next system component can immediately accept data once DAV goes active. The RMF flag has no internal action within the PDSP16540. SUPPORTING THE PDSP16510 The PDSP16510 FFT Processor does not contain sufficient RAM to allow it to perform continuous 1024 point transforms without ignoring some of the incoming data. When the PDSP16540 is used as an input buffer, continuous transforms can be executed without any loss of information. When block overlapping is not needed, or if the amount is restricted to either 50% or 75%, the mode control inputs can be directly used to define the operation of the PDSP16540. The D15:0 pins need not be used to define the block lengths.It should be noted, however, that the reset input is still needed to initialise the device, even though the state of the D15:0 pins is irelevent at that time. Figure 1 shows such a system. Tying MD0 low defines the block length to be 1024 words, and tying MD2:1 appropriately high or low will produce the required decodes to provide 0%, 50%, or 75% overlaps. With 50% overlapping 512 new words are loaded, and with 75% overlapping 256 new words are needed. MD5 should be tied low unless real only transformsd are to be done (See the next section). The DAV output is used to drive the INEN input on the PDSP16510 and the RMF flag is not used. The PDSDP16510 must be used in the mode in which INEN is an enabling signal, rather than its edge activated mode (Control Register Bit 12 must be set). The LFLG transition produced by the PDSP16510 is not used by the PDSP16540, since internal logic computes the starting address for the read operation.
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PDSP16540
SAMPLE CLOCK POWER ON RESET
SAMPLE CLOCK POWER ON RESET
510 PARAMETERS
GND GND
510 PARAMETERS
GND
GND
DAV DEF
GND
DEN
DAV
DEF
DEN
WEN WS IMAG'
RES AUX
WEN MD5
WS
RES AUX
INEN
SCLK
INEN
DIS
DOS
RS MD5:0 DAV GND
RS MD2:1 MD0 DAV +5V GND
SYSTEM CLOCK
SYSTEM CLOCK
5 BIT OVERLAP CODE
Figure 1. Typical 1024 Point FFT System
Figure 2 shows a 1024 point system which allows the amount of overlap to be any value within 32 words. The 5 bit overlap code defines groups of 32 new words which are written to the buffer, in addition to the minimum number of 32 words. The smaller the number of new words written, the greater is the overlap with the previous block. During reset the D31:0 outputs from the PDSP16540 will be high impedance and the 5 bit code is inputed on D9:5. This high impedance state also allows the PDSP16510 control parameters to be inputed on its AUX 15:0 bus without any conflicts. The rate at which data is written to the PDSP16540 must be such that 1024 words can be transferred between the devices, transformed , and then moved to the output circuit for analysis before the DAV flag goes active again. Since the read operation is interrupted for one cycle every time a write operation occurs, the equation controlling the minimum writing period is given by;
Figure 2. System with Non Standard Overlaps
NS > 1024B + 1024BS + T + D S-B where N is the amount of new data written to the buffer, S is the period of the write strobe, B is the read strobe period, T is the transform time as given in the data sheet for the PDSP16510, and D is the time to transfer data from the PDSP16510 to the next system device. It must be noted that the above minimum write period only applies if continuous inputs are to transformed without the loss of any incoming information. Peak writing rates can be much higher if gaps occur within the incoming data stream. The minimum periods given in Table 1 then limit the writing rate. When the PDSP16510 uses a 40 MHz clock, dumps its transformed data with a 40MHz strobe, and the PDSP16540 uses a 40 MHz read strobe, then the minimum S period is149 ns. This equates to a 6.7 MHz writing rate when blocks are not overlapped, 3.35 MHz with 50% overlaps ( 512 new words), or 1.675MHz with 75% overlaps ( 256 new words).
Characteristic RS Period,Tp RS Low Time RS High Time WS Period WS Period
Min 25ns 8ns 8ns 2Tp+10ns Tp x L N
Max
Notes
Both conditions must be satisfied L = Block length, N = amount of new data written
WS Low Time WS High Time WEN set up wrt WS going high WEN Hold wrt WS going high Data In Set Up wrt RS going high Data In Hold Time wrt RS going high Delay from RS going high to O/P Data
10ns 10ns 2 ns 8 ns 8 ns 0 ns 19ns 18ns 19ns 12ns All output delays are with 30pf loads Going active or in-active Occurs when DAV also goes active Occurs when DAV also goes in-active WEN going active or in-active
DAV,RMF transition wrt to RS going high 10ns Time to go Low Z wrt to RS going high Time to go High Z wrt to RS going high
Table 1. Timing Information
DIS
REAL
DOS
D
R
SCLK
PDSP16540 BUCKET BUFFER
I
IMAG'
PDSP16510
REAL
IP PDSP16540 D 31:16 BUCKET 31:16 BUFFER D IP 15:0 15:0
I
PDSP16510
D R
5
PDSP16540
The amount of overlapping is dependent on the needs of a particular application, and is usually subject to some compromise. If the above maximum writing rates are marginally not adequate, the amount of overlap can possibly be reduced to achieve the required performance. Mode control inputs MD2:1 should then all be tied high, and outputs D9:5 used as inputs during reset to define the number of new words to be written. SUPPORTING REAL ONLY TRANSFORMS If MD5 is tied high the PDSP16540 will support the PDSP16510 when two concurrent 1024 point real transaforms are to be performed. It does not suppoprt block overlapping in this mode. Real only data is written to the buffer using the IP15:0 inputs, and the IP31:16 inputs are redundant. Two blocks of data are acquired before DAV goes active, and both blocks are then read in parallel using all thirty two outputs. MD0,1, and 2 must be tied low in order to define blocks of 1024 words which totally consist of new data. The RMF flag is not needed by the PDSP16510, but will actually go active after the defined number of words in the second block have been loaded. Control Register Bits 8:6 in the PDSP16510 must be set to 101 in order to expect data on both its real and imaginary inputs.
ABSOLUTE MAXIMUM RATINGS [See Notes]
Supply voltage Vcc -0.5V to 7.0V Input voltage VIN -0.5V to Vcc + 0.5V Output voltage VOUT -0.5V to Vcc + 0.5V 18mA Clamp diode current per pin IK (see note 2) Static discharge voltage (HMB) 500V Storage temperature TS -65C to 150C Ambient temperature with power applied TAMB 0C to 70C Junction temperature 150C Package power dissipation 3000mW Thermal resistances Junction to case oJC 5C/W NOTES ON MAXIMUM RATINGS 1. Exceeding these ratings may cause permanent damage. Functional operation under these conditions is not implied. 2. Maximum dissipation or 1 second should not be exceeded, only one output to be tested at any one time. 3. Exposure to absolute maximum ratings for extended periods may affect device reliablity. 4. Current is defined as positive into the device.
Test
Waveform - measurement level
Delay from output high to output high impedance
VH
0.5V
Delay from output low to output high impedance
VL
0.5V
Delay from output high impedance to output low
1.5V
0.5V
Delay from output high impedance to output high
1.5V
0.5V
VH - Voltage reached when output driven high VL - Voltage reached when output driven low
STATIC ELECTRICAL CHARACTERISTICS
Operating Conditions (unless otherwise state) Tamb = 0 C to +70C. Vcc = 5.0v 10% Characteristic Symbol Min. Output high voltage Output low voltage Input high voltage Input low voltage Input leakage current Input capacitance Output leakage current Output S/C current VOH VOL VIH VIL IIN CIN IOZ ISC 2.4 2.8 -10 10 -50 10 +50 300 Value Typ. Units Max. 0.4 0.8 +10 V V V V A pF A mA IOH = 4mA IOL = -4mA GND < VIN < VCC GND < VOUT < VCC VCC = Max Conditions
6
PDSP16540
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PDSP16540
ORDERING INFORMATION
PDSP16540 PDSP16540 PDSP16540 PDSP16540 PDSP16540 C0 C0 B0 B0 A0 AC GC AC GC GC Commercial Commercial Industrial Industrial Military PGA package Ceramic QFP PGA package Ceramic QFP Ceramic QFP
HEADQUARTERS OPERATIONS GEC PLESSEY SEMICONDUCTORS Cheney Manor, Swindon, Wiltshire SN2 2QW, United Kingdom. Tel: (0793) 518000 Fax: (0793) 518411 GEC PLESSEY SEMICONDUCTORS P.O. Box 660017 1500 Green Hills Road, Scotts Valley, California 95067-0017, United States of America. Tel: (408) 438 2900 Fax: (408) 438 5576
CUSTOMER SERVICE CENTRES * FRANCE & BENELUX Les Ulis Cedex Tel: (1) 64 46 23 45 Tx: 602858F Fax : (1) 64 46 06 07 * GERMANY Munich Tel: (089) 3609 06-0 Tx: 523980 Fax : (089) 3609 06-55 * ITALY Milan Tel: (02) 66040867 Fax: (02) 66040993 * JAPAN Tokyo Tel: (03) 3296-0281 Fax: (03) 3296-0228 * NORTH AMERICA Integrated Circuits and Microwave Products Scotts Valley, USA Tel (408) 438 2900 Fax: (408) 438 7023. Hybrid Products, Farmingdale, USA Tel (516) 293 8686 Fax: (516) 293 0061. * SOUTH EAST ASIA Singapore Tel: (65) 3827708 Fax: (65) 3828872 * SWEDEN Stockholm, Tel: 46 8 702 97 70 Fax: 46 8 640 47 36 * UNITED KINGDOM & SCANDINAVIA Swindon Tel: (0793) 518510 Tx: 444410 Fax : (0793) 518582 These are supported by Agents and Distributors in major countries world-wide. (c) GEC Plessey Semiconductors 1995 Publication No. DS3715 Issue No. 1.1 February 1995
This publication is issued to provide information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose nor form part of any order or contract nor to be regarded as a representation relating to the products or services concerned. No warranty or guarantee express or implied is made regarding the capability, performance or suitability of any product or service. The Company reserves the right to alter without prior knowledge the specification, design or price of any product or service. Information concerning possible methods of use is provided as a guide only and does not constitute any guarantee that such methods of use will be satisfactory in a specific piece of equipment. It is the user's responsibility to fully determine the performance and suitability of any equipment using such information and to ensure that any publication or data used is up to date and has not been superseded. These products are not suitable for use in any medical products whose failure to perform may result in significant injury or death to the user. All products and materials are sold and services provided subject to the Company's conditions of sale, which are available on request.
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