GS81302T18GE-333I Datasheet, PDF (8/36 Pages) GSI Technology – 144Mb SigmaDDRTM-II Burst of 2 SRAM

GS81302T08/09/18/36E-375/350/333/300/250
Special Functions
Byte Write and Nybble Write Control
Byte Write Enable pins are sampled at the same time that Data In is sampled. A high on the Byte Write Enable pin associated with
a particular byte (e.g., BW0 controls D0–D8 inputs) will inhibit the storage of that particular byte, leaving whatever data may be
stored at the current address at that byte location undisturbed. Any or all of the Byte Write Enable pins may be driven high or low
during the data in sample times in a write sequence.
Each write enable command and write address loaded into the RAM provides the base address for a 2 beat data transfer. The x18
version of the RAM, for example, may write 36 bits in association with each address loaded. Any 9-bit byte may be masked in any
write sequence.
Nybble Write (4-bit) write control is implemented on the 8-bit-wide version of the device. For the x8 version of the device,
“Nybble Write Enable” and “NBx” may be substituted in all the discussion above.
Example x18 RAM Write Sequence using Byte Write Enables
Data In Sample Time
BW0
BW1
Beat 1
0
1
Beat 2
1
0
D0–D8
Data In
Don’t Care
D9–D17
Don’t Care
Data In
Resulting Write Operation
Byte 1
D0–D8
Written
Beat 1
Byte 2
D9–D17
Unchanged
Byte 3
D0–D8
Unchanged
Beat 2
Byte 4
D9–D17
Written
Output Register Control
SigmaDDR-II SRAMs offer two mechanisms for controlling the output data registers. Typically, control is handled by the Output
Register Clock inputs, C and C. The Output Register Clock inputs can be used to make small phase adjustments in the firing of the
output registers by allowing the user to delay driving data out as much as a few nanoseconds beyond the next rising edges of the K
and K clocks. If the C and C clock inputs isare tied high, the RAM reverts to K and K control of the outputs, allowing the RAM to
function as a conventional pipelined read SRAM.
FLXDrive-II Output Driver Impedance Control
HSTL I/O SigmaDDR-II SRAMs are supplied with programmable impedance output drivers. The ZQ pin must be connected to
V_SS via an external resistor, RQ, to allow the SRAM to monitor and adjust its output driver impedance. The value of RQ must be
5X the value of the desired RAM output impedance at mid-rail. The allowable range of RQ to guarantee impedance matching
continuously is between 175Ω and 350Ω. Periodic readjustment of the output driver impedance is necessary as the impedance is
affected by drifts in supply voltage and temperature. The SRAM’s output impedance circuitry compensates for drifts in supply
voltage and temperature. A clock cycle counter periodically triggers an impedance evaluation, resets and counts again. Each
impedance evaluation may move the output driver impedance level one step at a time towards the optimum level. The output driver
is implemented with discrete binary weighted impedance steps.
Rev: 1.03b 12/2011
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Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
© 2011, GSI Technology