47L64 datasheet(7/29 Pages) MICROCHIP

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2019-2020 Microchip Technology Inc.

Preliminary

DS20006168B-page 7

47L64

3.0

MEMORY ORGANIZATION

3.1

Data Array Organization

The 47L64 is internally organized as a continuous

SRAM array for both reading and writing, along with a

nonvolatile EEPROM version that is not directly

accessible to the user, but which can be refreshed or

recalled on power cycles.

3.2

STORE/RECALL OPERATIONS

In order to provide nonvolatile storage of the SRAM

data, an EEPROM array is included on the 47L64.

During normal operation, the EEPROM array is not

directly accessible to the user. Instead, the 47L64

preserves the SRAM data by automatically performing

store and recall operations on power-down and power-

up, respectively.

3.2.1

AUTOSTORE

To simplify device usage, the 47L64 features an

AutoStore mechanism. To enable this feature, the user

must place a capacitor on the VCAP pin. The capacitor

is charged through the VCC pin. When the 47L64

detects a power-down event, the device automatically

switches to the capacitor for power and initiates the

AutoStore operation.

To avoid extraneous store operations, the AutoStore

will only be initiated if the SRAM array has been

modified since the last Store or Recall operation.

The AutoStore is initiated when VCAP falls below

VTRIP. Even if power is restored, the 47L64 cannot be

accessed for TSTORE time and TRESTORE after the

AutoStore is initiated.

3.2.2

AUTORECALL

The 47L64

devices

features

an AutoRecall

mechanism that is performed on power-up. This

feature ensures that the SRAM data duplicates the

EEPROM data on power-up. The AutoRecall is

initiated when VCAP rises above VTRIP, and the 47L64

cannot be accessed for TRESTORE time after the

AutoRecall is initiated.

3.2.3

POLLING ROUTINE

Since the device will not acknowledge during store and

recall operations, checking for the Acknowledge signal

can be used to determine when those events are

complete. Once such an event has started,

Acknowledge polling can be initiated immediately. This

involves the master sending a Start condition, followed

by the write control byte (R/W = 0) for the SRAM array.

If the device is still busy, then no Acknowledge will be

returned. In this case, the Start condition and control

byte must be resent. If the Store or Recall are

complete, then the device will return an Acknowledge,

and the master can then proceed with the next read or

write command. See Figure 3-1 for flow diagram.

FIGURE 3-1:

POLLING FLOW

Note:

If power is restored during an AutoStore

operation, the AutoStore will continue and

then the AutoRecall will be performed.

Note 1: If power is lost during an AutoRecall

operation, the AutoRecall is aborted and

the AutoStore is not performed.

2: AutoRecall is performed every time VCAP

rises above VTRIP.

Send Start

Initiate SRAM

Write Event

Send Control Byte

with R/W = 0

Did Device

Acknowledge

(ACK = 0)?

Operation

YES

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