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DS1609
DS1609 Dual Port RAM
FEATURES
PIN ASSIGNMENT
PORT A AD7A AD6A AD5A AD4A AD3A AD2A AD1A AD0A WEA CEA OEA GND 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 PORT B VCC OEB CEB WEB AD0B AD1B AD2B AD3B AD4B AD5B AD6B AD7B
* Totally asynchronous 256-byte dual port memory * Multiplexed address
low and data bus keeps pin count
* Dual
port memory cell allows random access with minimum arbitration nals
* Each port has standard independent RAM control sig* Fast access time * Low power CMOS design * 24-pin DIP or 24-pin SOIC surface mount package * Both CMOS and TTL compatible * Operating temperature of -40C to +85C * Standby current of 100 nA @ 25C makes the device
ideal for battery backup or battery operate applications.
DS1609 24-PIN DIP (600 MIL) See Mech. Drawings Section PORT A AD7A AD6A AD5A AD4A AD3A AD2A AD1A AD0A WEA CEA OEA GND 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 PORT B VCC OEB CEB WEB AD0B AD1B AD2B AD3B AD4B AD5B AD6B AD7B
DS1609S 24-PIN SOIC (300 MIL) See Mech. Drawings Section
PIN DESCRIPTION
AD0-AD7 CE WE OE VCC GND - - - - - - Port address/data Port enable Write enable Output enable +5 volt supply Ground
DESCRIPTION
The DS1609 is a random access 256-byte dual port memory designed to connect two asyncronous address/data buses together with a common memory element. Both ports have unrestricted access to all 256 bytes of memory, and with modest system discipline no arbitration is required. Each port is controlled by three control signals: output enable, write enable, and port enable. The device is packaged in plastic 24-pin DIP and 24-pin SOIC. Output enable access time of 50 ns is available when operating at 5 volts.
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DS1609
OPERATION - READ CYCLE
The main elements of the dual port RAM are shown in Figure 1. A read cycle to either port begins by placing an address on the multiplexed bus pins AD0 - AD7. The port enable control (CE) is then transitioned low. This control signal causes address to be latched internally. Addresses can be removed from the bus provided address hold time is met. Next, the output enable control (OE) is transitioned low, which begins the data access portion of the read cycle. With both CE and OE active low, data will appear valid after the output enable access time tOEA. Data will remain valid as long as both port enable and output enable remains low. A read cycle is terminated with the first occurring rising edge of either CE or OE. The address/data bus will return to a high impedance state after time tCEZ or tOEZ as referenced to the first occurring rising edge. WE must remain high during read cycles.
WE active low the data to be written to the selected memory location is placed on the multiplexed bus. Provided that data setup (tDS) and data hold (tDH) times are met, data is written into the memory and the write cycle is terminated on the first occurring rising edge of either CE or WE. Data can be removed from the bus as soon as the write cycle is terminated. OE must remain high during write cycles.
ARBITRATION
The DS1609 dual port RAM has a special cell design that allows for simultaneous accesses from two ports (see Figure 2). Because of this cell design, no arbitration is required for read cycles occurring at the same instant. However, an argument for arbitration can be made for reading and writing the cell at the exact same instant or for writing from both ports at the same instant. A simple way to assure that read/write conflicts don't occur is to perform redundant read cycles. Write/write arbitration needs can be avoided by assigning groups of addresses for write operation to one port only. Groups of data can be assigned check sum bytes which would guarantee correct transmission. A software arbitration system using a "mail box" to pass status information can also be employed. Each port could be assigned a unique byte for writing status information which the other port would read. The status information could tell the reading port if any activity is in progress and indicate when activity is going to occur.
OPERATION - WRITE CYCLE
A write cycle to either port begins by placing an address on the multiplexed bus pins AD0 - AD7. The port enable control (CE) is then transitioned low. This control signal causes address to be latched internally. As with a read cycle, the address can be removed from the bus provided address hold time is met. Next the write enable control signal (WE) is transitioned low which begins the write data portion of the write cycle. With both CE and
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DS1609
BLOCK DIAGRAM: DUAL PORT RAM Figure 1
PORT A 8 ADDRESS MUX ADDRESS/DATA ADDRESS/ DATA MUX LATCH DECODE 8 DATA 8 ADDRESS ADDRESS/ DATA MUX LATCH DECODE 8 DATA MUX ADDRESS/DATA PORT B
256 BYTE DUAL PORT MEMORY MATRIX
WE OE CE CONTROL LOGIC CONTROL LOGIC
WE OE CE
DUAL PORT MEMORY CELL Figure 2
VCC
DATA-PORT A
DATA-PORT A
DATA-PORT B
DATA-PORT B
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DS1609
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -0.5V to +7.0V -40C to +85C -55C to +125C 260C for 10 seconds
* This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER Power Supply Input Logic 1 Input Logic 0 SYMBOL VCC VIH VIL MIN 4.5 2.0 -0.3 TYP 5.0 MAX 5.5 VCC + 0.3 +0.8
(-40C to +85C)
UNITS V V V NOTES 1 1 1
DC ELECTRICAL CHARACTERISTICS
PARAMETER Input Impedance CE, WE, OE Leakage Standby Current Standby Current Standby Current Operating Current Logic 1 Output Logic 0 Output SYMBOL ZIN ILO ICCS1 ICCS2 ICCS3 ICC VOH VOL 2.4 MIN 50K -1.0 3.0 50 100 18 TYP
(-40C to +85C; VCC = 5V 10%)
MAX UNITS +1.0 5.0 300 A mA A nA 30 mA V 0.4 V 3, 4, 13 3, 5, 13 3, 6, 13 7, 13 8 9 NOTES 2
CAPACITANCE
PARAMETER Input Capacitance I/O Capacitance SYMBOL CIN CI/O MIN TYP 5 5 MAX 10 10 UNITS pF pF
(tA = 25C)
NOTES
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DS1609
AC ELECTRICAL CHARACTERISTICS
PARAMETER Address Setup Time Address Hold Time Output Enable Access OE to High Z CE to High Z Data Setup Time Data Hold Time Write Pulse Width CE Recovery Time WE Recovery Time OE Recovery Time CE to OE Setup Time CE to WE Setup Time SYMBOL tAS tAH tOEA tOEZ tCEZ tDS tDH tWP tCER tWER tOER tCOE tCWE MIN 5 25 0 0 0 0 10 50 20 20 20 25 25 TYP
(-40C to +85C; VCC = 5V 10%)
MAX UNITS ns ns 50 20 20 ns ns ns ns ns ns ns ns ns ns ns 11 12 12 12 10 NOTES
AC ELECTRICAL CHARACTERISTICS
PARAMETER Address Setup Time Address Hold Time Output Enable Access OE to High Z CE to High Z Data Setup Time Data Hold Time Write Pulse Width CE Recovery Time WE Recovery Time OE Recovery Time CE to OE Setup Time CE to WE Setup Time SYMBOL tAS tAH tOEA tOEZ tCEZ tDS tDH tWP tCER tWER tOER tCOE tCWE MIN 5 25 0 0 0 0 10 100 20 20 20 25 25 TYP
(-40C to +85C; VCC = 2.5V - 4.5V)
MAX UNITS ns ns 100 20 20 ns ns ns ns ns ns ns ns ns ns ns 11 12 12 12 10 NOTES
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DS1609
DUAL PORT RAM TIMING: READ CYCLE DURING READ CYCLE WE = VIH
AD0 - AD7 tAS
ADDRESS VALID
DON'T CARE
DATA OUT VALID
tAH CE
tCEZ
tCOE tOEA OE tOEZ
NOTES:
1. During read cycle the address must be off the bus prior to tOEA minimum to avoid bus contention. 2. Read cycles are terminated by the first occurring rising edge of OE or CE.
DUAL PORT RAM TIMING: WRITE CYCLE DURING WRITE CYCLE OE = VIH
AD0 - AD7 tAS
ADDRESS VALID
DON'T CARE
DATA IN VALID
tAH CE
tCWE tDS WE tWP tDH
NOTE:
1. Write cycles are terminated by the first occurring edge of WE or CE.
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DS1609
NOTES:
1. All Voltages are referenced to ground. 2. All pins other than CE, WE, OE, VCC and ground are continuously driven by a feedback latch in order to hold the inputs at one power supply rail or the other when an input is tristated. The minimum driving impedance presented to any pin is 50K. If a pin is at a logic low level, this impedance will be pulling the pin to ground. If a pin is at a logic high level, this impedance will be pulling the pin to VCC. 3. Standby current is measured with outputs open circuited. 4. ICCS1 is measured with all pins within 0.3V of VCC or GND and with CE at a logic high or logic low level. 5. ICCS2 is measured with all pins within 0.3V of VCC or ground and with CE within 0.3V of VCC. 6. ICCS3 is measured with all pins at VCC or ground potential and with CE = VCC. Note that if a pin is floating, the internal feedback latches will pull all the pins to one power supply rail or the other. 7. Active current is measured with outputs open circuited, and inputs swinging full supply levels with one port reading and one port writing at 100 ns cycle time. Active currents are a DC average with respect to the number of 0's and 1's being read or written. 8. Logic one voltages are specified at a source current of 1 mA. 9. Logic zero voltages are specified at a sink current of 4 mA. 10. Measured with a load as shown in Figure 3. 11. tWP is defined as the time from WE going low to the first of the rising edges of WE and CE. 12. Recovery time is the amount of time control signals must remain high between successive cycles. 13. Typical values are at 25C.
LOAD SCHEMATIC Figure 3
+5 VOLTS
1.1K
D.U.T.
680
30 pF
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