S71PL254 datasheet(188/196 Pages) SPANSION

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188

pSRAM Type 1

pSRAM_Type01_12_A0 June 8, 2004

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I n f o rmation

Power Savings Modes (For 16M Page Mode, 32M and 64M Only)

There are several power savings modes.

Partial Array Self Refresh

Temperature Compensated Refresh (64M)

Deep Sleep Mode

Reduced Memory Size (32M, 16M)

The operation of the power saving modes ins controlled by the settings of bits

contained in the Mode Register. This definition of the Mode Register is shown in

Figure 93 and the various bits are used to enable and disable the various low

power modes as well as enabling Page Mode operation. The Mode Register is set

by using the timings defined in Figure xxx.

Partial Array Self Refresh (PAR)

In this mode of operation, the internal refresh operation can be restricted to a

16Mb, 32Mb, or 48Mb portion of the array. The array partition to be refreshed is

determined by the respective bit settings in the Mode Register. The register set-

tings for the PASR operation are defined in Table xxx. In this PASR mode, when

ZZ# is active low, only the portion of the array that is set in the register is re-

freshed. The data in the remainder of the array will be lost. The PASR operation

mode is only available during standby time (ZZ# low) and once ZZ# is returned

high, the device resumes full array refresh. All future PASR cycles will use the

contents of the Mode Register that has been previously set. To change the ad-

dress space of the PASR mode, the Mode Register must be reset using the

previously defined procedures. For PASR to be activated, the register bit, A4Must

be set to a one (1) value, “PASR Enabled”. If this is the case, PASR will be acti-

vated 10 µs after ZZ# is brought low. If the A4 register bit is set equal to zero

(0), PASR will not be activated.

Temperature Compensated Refresh (for 64Mb)

In this mode of operation, the internal refresh rate can be optimized for the op-

eration temperature used and this can then lower standby current. The DRAM

array in the PSRAM must be refreshed internally on a regular basis. At higher

temperatures, the DRAM cell must be refreshed more often than at lower tem-

peratures. By setting the temperature of operation in the Mode Register, this

refresh rate can be optimized to yield the lowest standby current at the given op-

erating temperature. There are four different temperature settings that can be

programmed in to the PSRAM. These are defined in Figure 93.

Deep Sleep Mode

In this mode of operation, the internal refresh is turned off and all data integrity

of the array is lost. Deep Sleep is entered by bringing ZZ# low with the A4 reg-

ister bit set to a zero (0), “Deep Sleep Enabled”. If this is the case, Deep Sleep

will be entered 10 µs after ZZ# is brought low. The device will remain in this mode

as long as ZZ# remains low. If the A4 register bit is set equal to one (1), Deep

Sleep will not be activated.

Reduced Memory Size (for 32M and 16M)

In this mode of operation, the 32Mb PSRAM can be operated as a 8Mb or 16Mb

device. The mode and array size are determined by the settings in the VA register.

The VA register is set according to the following timings and the bit settings in

the table “Address Patterns for RMS”. The RMS mode is enabled at the time of ZZ

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