PSD4235G2 datasheet(27/89 Pages) STMICROELECTRONICS

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PSD4235G2

entitled “Programming Flash Memory”, on page

25. The Error Flag (DQ5/DQ13) bit returns a 1 if

there has been an Erase Failure (maximum num-

ber of Erase cycles have 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 instruc-

tion uses six Write operations, as described in Ta-

ble 29. Additional Flash Sector Erase confirm

commands and Flash memory sector addresses

can be written subsequently to erase other Flash

memory sectors in parallel, without further coded

cycles, if the additional commands are transmitted

in a shorter time than the time-out period of about

100 µs. 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 (DQ3/

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

bit is 0, the Sector Erase instruction has been re-

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

Erase Time-out Flag (DQ3/DQ11) bit 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 (DQ5/DQ13)

bit, the Toggle Flag (DQ6/DQ14) bit, and the Data

Polling (DQ7/DQ15) bit, as detailed in the section

entitled “Programming Flash Memory”, on page

25.

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 Suspend Sector Erase in-

struction can be used to suspend the cycle by writ-

ing

0B0h

any

even

address

when

appropriate

Sector

Select

(FS0-FS7

CSBOOT0-CSBOOT3) is High. (See Table 29).

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 instruction ex-

ecution and defaults to Read mode. A Suspend

Sector Erase instruction executed during an Erase

time-out period, in addition to suspending the

Erase cycle, terminates the time out period.

The Toggle Flag (DQ6/DQ14) bit 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 (DQ6/DQ14) bit stops toggling be-

tween 0.1 µs and 15 µs 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 al-

lowed).

– If a Reset instruction is received, data in the

Flash memory sector that was being erased is

invalid.

Resume Sector Erase. If

Suspend

Sector

Erase instruction was previously executed, the

Erase cycle may be resumed with this instruction.

The Resume Sector Erase instruction consists of

writing 030h to any even address while an appro-

priate Sector Select (FS0-FS7 or CSBOOT0-

CSBOOT3) is High. (See Table 29.)

Flash Memory Sector Protect

Each sector of Primary or Secondary Flash mem-

ory can be separately protected against Program

and Erase cycles. Sector Protection provides ad-

ditional data security because it disables all Pro-

gram or Erase cycles. This mode can be activated

(or deactivated) through the JTAG-ISP Port or a

Device Programmer.

Sector protection can be selected for each sector

using the PSDsoft Express program. This auto-

matically protects selected sectors when the de-

vice is programmed through the JTAG Port or a

Device Programmer. Flash memory sectors can

be unprotected to allow updating of their contents

using the JTAG Port or a Device Programmer. The

MCU can read (but cannot change) the sector pro-

tection bits.

Any attempt to program or erase a protected Flash

memory sector is ignored by the device. The Verify

operation results in a read of the protected data.

This allows a guarantee of the retention of the Pro-

tection status.

The sector protection status can be read by the

MCU through the Flash memory protection and

Secondary Flash memory protection registers (in

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