PSD4235G2V-10UI datasheet(33/100 Pages) STMICROELECTRONICS

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PSD4256G6V

This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.

ERASING FLASH MEMORY

Flash Bulk Erase

The Flash Bulk Erase instruction uses six WRITE

operations followed by a READ operation of the

status register, as described in Table 29, page 27.

If any byte of the Bulk Erase instruction is wrong,

the Bulk Erase instruction aborts and the device is

reset to the READ Memory mode.

During a Bulk Erase, the memory status may be

checked by reading the Error Flag Bit (DQ5/

DQ13), the Toggle Flag Bit (DQ6/DQ14), and the

Data Polling Bit (DQ7/DQ15), as detailed in the

section entitled “PROGRAMMING FLASH MEM-

ORY”, on page 31. The Error Flag Bit (DQ5/DQ13)

returns a '1' if there has been an Erase Failure

(maximum number of Erase cycles have been ex-

ecuted).

It is not necessary to program the memory with

00h because the PSD automatically does this be-

fore erasing to 0FFh.

During execution of the Bulk Erase instruction, the

Flash memory does not accept any instructions.

Flash Sector Erase

The Sector Erase instruction uses six WRITE op-

erations, as described in Table 29, page 27. Addi-

tional Flash Sector Erase confirm commands and

Flash memory sector addresses can be written

subsequently to erase other Flash memory sec-

tors in parallel, without further coded cycles, if the

additional commands are transmitted in a shorter

time than the time-out period of about 100µs. The

input of a new Sector Erase command restarts the

time-out period.

The status of the internal timer can be monitored

through the level of the Erase Time-out Flag Bit

(DQ3/DQ11). If the Erase Time-out Flag Bit (DQ3/

DQ11) is '0,' the Sector Erase instruction has been

received and the time-out period is counting. If the

Erase Time-out Flag Bit (DQ3/DQ11) is '1,' the

time-out period has expired and the PSD is busy

erasing the Flash memory sector(s). Before and

during Erase time-out, any instruction other than

Suspend Sector Erase and Resume Sector Erase,

abort the cycle that is currently in progress, and re-

set the device to READ Mode. It is not necessary

to program the Flash memory sector with 00h as

the PSD does this automatically before erasing.

During a Sector Erase, the memory status may be

checked by reading the Error Flag Bit (DQ5/

DQ13), the Toggle Flag Bit (DQ6/DQ14), and the

Data Polling Bit (DQ7/DQ15), as detailed in the

section entitled “PROGRAMMING FLASH MEM-

ORY”, on page 31.

During execution of the Erase cycle, the Flash

memory accepts only RESET and Suspend Sec-

tor Erase instructions. Erasure of one Flash mem-

ory sector may be suspended, in order to read

data from another Flash memory sector, and then

resumed.

Suspend Sector Erase

When a Sector Erase cycle is in progress, the Sus-

pend Sector Erase instruction can be used to sus-

pend the cycle by writing 0B0h to any even

address when an appropriate Sector Select (FS0-

FS15 or CSBOOT0-CSBOOT3) is High. (See Ta-

ble 29, page 27). This allows reading of data from

another Flash memory sector after the Erase cycle

has been suspended. Suspend Sector Erase is

accepted only during the Flash Sector Erase in-

struction execution and defaults to READ Mode. A

Suspend Sector Erase instruction executed during

an Erase time-out period, in addition to suspend-

ing the Erase cycle, terminates the time out period.

The Toggle Flag Bit (DQ6/DQ14) stops toggling

when the PSD internal logic is suspended. The

status of this bit must be monitored at an address

within the Flash memory sector being erased. The

Toggle Flag Bit (DQ6/DQ14) stops toggling be-

tween 0.1µs and 15µs after the Suspend Sector

Erase instruction has been executed. The PSD is

then automatically set to READ Mode.

If an Suspend Sector Erase instruction was exe-

cuted, the following rules apply:

– Attempting to read from a Flash memory sector

that was being erased outputs invalid data.

– Reading from a Flash memory sector that was

not being erased is valid.

– The Flash memory

cannot be programmed, and

only responds to Resume Sector Erase and RE-

SET instructions (READ is an operation and is

allowed).

–If a RESET instruction is received, data in the

Flash memory sector that was being erased is

invalid.

Resume Sector Erase

If a Suspend Sector Erase instruction was previ-

ously executed, the Erase cycle may be resumed

with this instruction. The Resume Sector Erase in-

struction consists of writing 030h to any even ad-

dress while an appropriate Sector Select (FS0-

FS15 or CSBOOT0-CSBOOT3) is High. (See Ta-

ble 29, page 27.)

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