UPSD325X datasheet(113/176 Pages) STMICROELECTRONICS

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µPSD325X DEVICES

Data Toggle. Checking

the

Toggle

Flag

Bit

(DQ6) is a method of determining whether a Pro-

gram or Erase cycle is in progress or has complet-

ed. Figure 53 shows the Data Toggle algorithm.

When the MCU issues a Program instruction, the

embedded algorithm begins. The MCU then reads

the location of the byte to be programmed in Flash

memory to check status. The Toggle Flag Bit

(DQ6) of this location toggles each time the MCU

reads this location until the embedded algorithm is

complete. The MCU continues to read this loca-

tion, checking the Toggle Flag Bit (DQ6) and mon-

itoring the Error Flag Bit (DQ5). When the Toggle

Flag Bit (DQ6) stops toggling (two consecutive

reads yield the same value), and the Error Flag Bit

(DQ5) remains ’0,’ the embedded algorithm is

complete. If the Error Flag Bit (DQ5) is ’1,’ the

MCU should test the Toggle Flag Bit (DQ6) again,

since the Toggle Flag Bit (DQ6) may have

changed simultaneously with the Error Flag Bit

(DQ5) (see Figure 53).

The Error Flag Bit(DQ5) 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 53 still applies. the Toggle

Flag Bit (DQ6) toggles until the Erase cycle is

complete. A 1 on the Error Flag Bit (DQ5) indicates

a time-out condition on the Erase cycle; a ’0’ indi-

cates no error. The MCU can read any location

within the sector being erased to get the Toggle

Flag Bit (DQ6) and the Error Flag Bit (DQ5).

PSDsoft Express generates ANSI C code func-

tions which implement these Data Toggling algo-

rithms.

Figure 53. Data Toggle Flowchart

READ

DQ5 & DQ6

START

READ DQ6

FAIL

PASS

AI01370B

DQ6

TOGGLE

YES

DQ5

= 1

YES

DQ6

TOGGLE

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