48LM01 datasheet(23/40 Pages) MICROCHIP

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DS20006008C-page 23

48L512/48LM01

11.0 STORE/RECALL OPERATIONS

This EERAM device is intended to be serial SRAM

with internal management of all backup transfers to

and from EEPROM on power disruption, so the

EEPROM portion of the SRAM memory cell is not

directly

accessible

the

user.

However,

user-managed Software Store and Software Recall

commands are included. The factory default for the

ASE bit in the STATUS register is ‘0’, enabling the

AutoStore function.

11.1

Automatic Store on Any Power

Disruption

To enable this feature, the user must place a capacitor

on the VCAP pin and ensure the ASE bit in the

STATUS register is set to ‘0’. The capacitor is charged

through the VCC pin. When the 48LXXX detects a

power-down event, the device automatically switches

to the capacitor for power and initiates the AutoStore

operation.

Note that to minimize the transfer events to EEPROM,

this automatic store will only be initiated if the SRAM

array has been modified since the last store or recall

operation.

The automatic store cycle (AutoStore) is initiated when

VCAP falls below VTRIP. Even if power is restored, the

48LXXX cannot be accessed for TSTORE time after the

AutoStore is initiated.

11.2

Automatic Recall to SRAM

An automatic recall of EEPROM to SRAM (AutoRe-

call) is performed on power-up, regardless of the state

of the ASE bit. 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 48LXXX cannot be accessed for TRESTORE

time after the AutoRecall is initiated.

11.3

Software Store Command

The Software Store command must be user-initiated

and will store the contents of the SRAM bits, the

nonvolatile user space, and the Configuration bits of

the STATUS register (BP[1:0] and ASE) into

nonvolatile storage. The Software Store command

functions even if the contents of the array and regis-

ters have not changed since the last store or recall.

Reading the STATUS register during the store cycle

will indicate a busy bit. Other operations will be

ignored.

FIGURE 11-1:

SOFTWARE STORE

Note: If power is restored during an AutoStore

operation, the AutoStore will continue

and

the

AutoRecall

will

not

performed because the SRAM content

is still valid.

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.

SCK

345

High-Impedance

STORE Opcode

000

MSb

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