PSD853F5A-70UI View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

PSD853F5A-70UI

Flash in-system programmable (ISP) peripherals for 8-bit MCUs, 5 V

STMicroelectronics 

PSD8XXFX

Figure 6. Data Polling flowchart

START

READ DQ5 & DQ7

at VALID ADDRESS

Programming Flash memory

DQ7

=

YES

DATA

NO

NO DQ5

=1

YES

READ DQ7

DQ7

=

YES

DATA

NO

FAIL

PASS

AI01369B

8.2

Data Toggle

Checking the Toggle flag bit (DQ6) is a method of determining whether a program or erase

cycle is in progress or has completed. Figure 7 shows the Data Toggle algorithm.

When the MCU issues a Program instruction, the embedded algorithm within the PSD

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

location, checking the Toggle flag bit (DQ6) and monitoring 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 7).

The Error flag bit (DQ5) is set if either an internal timeout occurred while the embedded

algorithm attempted to program the byte, or if the MCU attempted 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

programming 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 7 still applies. the Toggle

flag bit (DQ6) toggles until the Erase cycle is complete. A '1' on the Error flag bit (DQ5)

indicates a timeout condition on the Erase cycle; a '0' indicates no error. The MCU can read

Doc ID 7833 Rev 7

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