M39208 datasheet(11/30 Pages) STMICROELECTRONICS

11 / 30 page

Data Polling. Polling on DQ7 is a method of check-

ing whether a Program or an Erase instruction is in

progress or completed (see Figure 6). When a

Program instruction is in progress, data bit DQ7 is

the complement of the original data bit 7; when

DQ7 is identical to the old data and the Error bit

DQ5 is still ’0’, the instruction is complete. To de-

termine if DQ7 is valid, each poll must store the

original data for comparison, and if they are the

same, it can be considered that the operation was

successful. The Error bit DQ5 is checked to ensure

timing limits have not exceeded.

When an Erase operation is in progress, DQ7 is

always ’0’, and will be ’1’ when finished, so long as

DQ5= ’0’.

In all cases, when DQ5 is ’1’, DQ7 should be

checked again, in case DQ7 changed simultane-

ously with DQ5. If DQ7 = true data (Program) or

DQ7 = ’1’ (Erase), the operation is successful and

execution should return to the caller. A suggested

second read will provide all true data (Program) or

all FFh (Erase). Otherwise, this should be flagged

as an error, and the device should be Reset.

Data Toggle. Checking the Toggle bit DQ6 is an

alternative method of checking if Program or Erase

operations are in progress or completed (see Fig-

ure 7). When an operation is in progress, data bit

DQ6 constantly toggles for successive read opera-

tions. When DQ6 no longer toggles and the Error

bit DQ5 is ’0’, the operation is completed. To deter-

mine if DQ6 has toggled, each polling action re-

quires 2 consecutive read operations of the data,

and if the data read is the same, it can be consid-

ered that the operation was successful. The Error

bit DQ5 is checked to ensure timing limits have not

been exceeded. In all cases, when DQ5 is ’1’, DQ6

should be checked again, in case DQ6 has

changed simultaneously with DQ5. If DQ6 has

stopped toggling, the operation is successful and

execution should return to the caller. A suggested

second read will provide all true data (Program) or

all FFh (Erase). Otherwise, this event should be

flagged as an error, and the device should be

Reset.

ERASE in the Flash BLOCK

It should be noted that:

a. Programming any byte of one Flash sector (or

bulk) requires that the Flash sector (or bulk) has

been previously erased (once for all bytes within

the sector or bulk) with the correct instruction (see

Instructions chapter).

b. Writing in the EEPROM memory is an operation

triggering an automatic sequencing of byte erase

followed by a byte write. Writing in EEPROM does

not require a specific erase operation before writ-

ing.

Bulk Erase Instruction. The Bulk Erase instruc-

tion uses six write operations followed by Read

operations of the status register bits, as described

in Table 4. If any byte of the Bulk Erase instruction

is wrong, the Bulk Erase instruction aborts and the

device is reset to the Read Flash memory status.

During a Bulk Erase, the memory status may

checked by reading the status bits DQ5, DQ6 and

DQ7, as detailed in the "PROGRAM in the Flash

BLOCK" chapter. The Error bit (DQ5) 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 array with 00h,

the M39208 will automatically do this before eras-

ing to FFh.

During the execution of the Bulk Erase instruction,

the Flash block logic does not accept any instruc-

tion.

Sector Erase in Flash Block. The Sector Erase

instruction uses six write operations, as described

in Table 4. Additional Flash Sector Erase confirm

commands and Flash sector addresses can written

subsequently to erase other Flash sectors in par-

allel, without further coded cycles, if the additional

instruction is transmited in a shorter time than the

timeout period to end of period. The input of a new

Sector Erase instruction will restart the time-out

period.

The status of the internal timer can be monitored

through the level of DQ3 (Erase time-out bit), if DQ3

is ’0’ the Sector Erase instruction has been re-

ceived and the timeout is counting; if DQ3 is ’1’, the

timeout has expired and the M39208 is erasing the

Flash sector(s). Before and during Erase timeout,

any instruction different than Erase suspend and

Erase Resume will abort the instruction and reset

the device to read array mode.

It is not necessary to program the Flash sector with

00h as the M39208 will do this automatically before

erasing (byte = FFh).

During a Sector Erase, the memory status may be

checked by reading the status bits DQ5, DQ6 and

DQ7, as detailed in the "Program instruction" chap-

ter. During the execution of the erase instruction,

the Flash block logic accepts only the Reset and

Erase Suspend instructions (erasure of one Flash

sector may be suspended, in order to read data

from another Flash sector, and then resumed).

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