PSD835G2 datasheet(33/102 Pages) STMICROELECTRONICS

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PSD835G2

ERASING FLASH MEMORY

Flash Bulk Erase

The Flash Bulk Erase instruction uses six WRITE

operations followed by a READ operation of the

status

described

Table

28., page 27. If any byte of the Bulk Erase instruc-

tion is wrong, the Bulk Erase instruction aborts and

the device is reset to the Read Flash memory sta-

tus.

During a Bulk Erase, the memory status may be

checked by reading the Error Flag Bit (DQ5), the

Toggle Flag Bit (DQ6), and the Data Polling Flag

Bit (DQ7), as detailed in “PROGRAMMING

FLASH MEMORY, page 31. The Error Flag Bit

(DQ5) returns a ’1’ if there has been an Erase Fail-

ure (maximum number of Erase cycles has been

executed).

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 28., page 27. Addi-

tional Flash Sector Erase codes and Flash

memory sector addresses can be written subse-

quently to erase other Flash memory sectors in

parallel, without further coded cycles, if the addi-

tional bytes are transmitted in a shorter time than

the time-out period of about 100µs. The input of a

new Sector Erase code restarts the time-out peri-

od.

The status of the internal timer can be monitored

through the level of the Erase Time-out Flag Bit

(DQ3). If the Erase Time-out Flag Bit (DQ3) is '0,'

the Sector Erase instruction has been received

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

Time-out Flag Bit (DQ3) 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 instructions

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

(Byte=FFh).

During a Sector Erase, the memory status may be

checked by reading the Error Flag Bit (DQ5), the

Toggle Flag Bit (DQ6), and the Data Polling Flag

Bit (DQ7), as detailed in PROGRAMMING FLASH

MEMORY, page 31.

During execution of the Erase cycle, the Flash

memory accepts only Reset and Suspend Sector

Erase instructions. Erasure of one Flash memory

sector may be suspended, in order to read data

from another Flash memory sector, and then re-

sumed.

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-

FS7 or CSBOOT0-CSBOOT3) is High. (See Table

28., page 27). This allows reading of data from an-

other Flash memory sector after the Erase cycle

has been suspended. Suspend Sector Erase is

accepted only during an Erase cycle and defaults

to READ mode. A Suspend Sector Erase instruc-

tion executed during an Erase time-out period, in

addition to suspending the Erase cycle, terminates

the time out period.

The Toggle Flag Bit (DQ6) 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) stops toggling between 0.1µs and

15µs after the Suspend Sector Erase instruction

has been executed. The PSD is then automatically

set to READ mode.

If a Suspend Sector Erase instruction was execut-

ed, the following rules apply:

– Attempting to read from a Flash memory sector

that was being erased outputs invalid data.

– Reading from a Flash sector that was not being

erased is valid.

– The Flash memory cannot be programmed, and

only responds to Resume Sector Erase and Re-

set Flash instructions (READ is an operation

and is allowed).

– If a Reset Flash 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 in writing 030h to any even ad-

dress while an appropriate Sector Select (FS0-

FS7 or CSBOOT0-CSBOOT3) is High. (See Table

28., page 27.)

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