PSD834210MIT datasheet(20/89 Pages) STMICROELECTRONICS

20 / 89 page

PSD834F2V

20/89

Figure 5. Data Toggle Flowchart

The Error Flag (DQ5) bit is set if either an internal

time-out occurred while the embedded algorithm

attempted to program the byte, or if the MCU at-

tempted to program a 1 to a bit that was not erased

(not erased is logic 0).

It is suggested (as with all Flash memories) to read

the location again after the embedded program-

ming algorithm has completed, to compare the

byte that was written to Flash memory with the

byte that was intended to be written.

When using the Data Toggle method after an

Erase cycle, Figure 5 still applies. the Toggle Flag

(DQ6) bit toggles until the Erase cycle is complete.

A 1 on the Error Flag (DQ5) bit indicates a time-out

condition on the Erase cycle; a 0 indicates no er-

ror. The MCU can read any location within the sec-

tor being erased to get the Toggle Flag (DQ6) bit

and the Error Flag (DQ5) bit.

PSDsoft Express generates ANSI C code func-

tions which implement these Data Toggling algo-

rithms.

Unlock Bypass. The Unlock Bypass instructions

allow the system to program bytes to the Flash

memories faster than using the standard Program

instruction. The Unlock Bypass mode is entered

by first initiating two Unlock cycles. This is followed

by a third Write cycle containing the Unlock By-

pass code, 20h (as shown in Table 7).

The Flash memory then enters the Unlock Bypass

mode. A two-cycle Unlock Bypass Program in-

struction is all that is required to program in this

mode. The first cycle in this instruction contains

the Unlock Bypass Program code, A0h. The sec-

ond cycle contains the program address and data.

Additional data is programmed in the same man-

ner. These instructions dispense with the initial

two Unlock cycles required in the standard Pro-

gram instruction, resulting in faster total Flash

memory programming.

During the Unlock Bypass mode, only the Unlock

Bypass Program and Unlock Bypass Reset Flash

instructions are valid.

To exit the Unlock Bypass mode, the system must

issue the two-cycle Unlock Bypass Reset Flash in-

struction. The first cycle must contain the data

90h; the second cycle the data 00h. Addresses are

Don’t Care for both cycles. The Flash memory

then returns to Read mode.

Erasing Flash Memory

Flash Bulk Erase. The Flash Bulk Erase instruc-

tion uses six Write operations followed by a Read

operation of the status register, as described in

Table 7. 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 be

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

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

(DQ7) bit, as detailed in the section entitled “Pro-

gramming Flash Memory”, on page 19. The Error

Flag (DQ5) bit returns a 1 if there has been an

Erase Failure (maximum number 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 7. Additional Flash Sector Erase codes 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 bytes are transmitted in a shorter time

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

of a new Sector Erase code restarts the time-out

period.

The status of the internal timer can be monitored

through the level of the Erase Time-out Flag (DQ3)

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

Sector Erase instruction has been received and

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

out Flag (DQ3) bit is 1, the time-out period has ex-

pired and the PSD is busy erasing the Flash mem-

READ

DQ5 & DQ6

START

READ DQ6

FAIL

PASS

AI01370B

DQ6

TOGGLE

YES

DQ5

= 1

YES

DQ6

TOGGLE

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