S71GS256 datasheet(114/195 Pages) SPANSION

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114

CellularRAM Type 2

cellRAM_00_A0 October 4, 2004

Advan ce

In form ati o n

Low-Power Operation

Standby Mode Operation

During standby, the device current consumption is reduced to the level necessary

to perform the DRAM refresh operation. Standby operation occurs when CE# is

HIGH.

The device will enter a reduced power state upon completion of a READ or WRITE

operation, or when the address and control inputs remain static for an extended

period of time. This mode will continue until a change occurs to the address or

control inputs.

Temperature Compensated Refresh

Temperature compensated refresh (TCR) is used to adjust the refresh rate de-

pending on the device operating temperature. DRAM technology requires

increasingly frequent refresh operation to maintain data integrity as tempera-

tures increase. More frequent refresh is required due to increased leakage of the

DRAM capacitive storage elements as temperatures rise. A decreased refresh rate

at lower temperatures will facilitate a savings in standby current.

TCR allows for adequate refresh at four different temperature thresholds (+15

°C,

+45

°C, +70°C, and +85°C). The setting selected must be for a temperature

higher than the case temperature of the CellularRAM device. For example, if the

case temperature is 50

°C, the system can minimize self refresh current con-

sumption by selecting the +7

°0C setting. The +15°C and +45°C settings would

result in inadequate refreshing and cause data corruption.

Note: Non-default BCR settings: Latency code two (three clocks); WAIT active LOW; WAIT asserted during delay.

Figure 30. Refresh Collision During WRITE Operation

Address

Valid

Additional WAIT states inserted to allow refresh completion.

CLK

A[22:0]

ADV#

CE#

OE#

WE#

WAIT

DQ[15:0]

LB#/UB#

Don't care

Legend:

VIH

VIL

VIH

VIL

VIH

VIL

VIH

VIL

VIH

VIL

VIH

VIL

VIH

VIL

High-Z

VOH

VOL

D[1]

D[2]

D[3]

VOH

VOL

D[0]

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