IS61QDB24M18A

IS61QDB22M36A

Integrated Silicon Solution, Inc.- www.issi.com

Rev. A

8/7/2014

5

During a write, the byte writes independently control which byte of any of the four burst addresses is written (see

X18/X36 Write Truth Tables and Timing Reference Diagram for Truth Table).

Whenever a write is disabled (W# is high at the rising edge of K), data is not written into the memory.

RQ Programmable Impedance

its output driver impedance. The value of RQ must be 5x the value of the intended line impedance driven by the

SRAM. For example, an RQ

of 250Ω results in a driver impedance of 50Ω. The allowable range of RQ to guarantee

impedance matching is between 175Ω and 350Ω at V

away from the ZQ ball on the SRAM module. The capacitance of the loaded ZQ trace must be less than 7.5pF.

PROGRAMMABLE IMPEDANCE AND POWER-UP REQUIREMENT

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Periodic readjustment of the output driver impedance is necessary as the impedance is greatly affected by drifts in

supply voltage and temperature. During power-up, the driver impedance is in the middle of allowable impedances

values. The final impedance value is achieved within 1024 clock cycles.

Single Clock Mode

This device can be also operated in single-clock mode. In this case, C and C# are both connected high at power-up

and must never change. Under this condition, K and K# will control the output timings.

clocks.

Depth Expansion

Separate input and output ports enable easy depth expansion, as each port can be selected and deselected

independently. Read and write operations can occur simultaneously without affecting each other. Also, all pending

read and write transactions are always completed prior to deselecting the corresponding port.

Delay Locked Loop (DLL)

Delay Locked Loop (DLL) is a new system to align the output data coincident with clock rising or falling edge to

enhance the output valid timing characteristics. It is locked to the clock frequency and is constantly adjusted to match

the clock frequency. Therefore device can have stable output over the temperature and voltage variation.

DLL has a limitation of locking range and jitter adjustment which are specified as tKHKH and tKCvar respectively in the

AC timing characteristics. In order to turn this feature off, applying logic low to the Doff# pin will bypass this. In the DLL

off mode, the device behaves with one cycle latency and a longer access time which is known in DDR-I or legacy

QUAD mode.

The DLL can also be reset without power down by toggling Doff# pin low to high or stopping the input clocks K and K#

for a minimum of 30ns.(K and K# must be stayed either at higher than VIH or lower than VIL level. Remaining Vref is

not permitted.) DLL reset must be issued when power up or when clock frequency changes abruptly. After DLL being

reset, it gets locked after 2048 cycles of stable clock.