UPSD325X datasheet(112/176 Pages) STMICROELECTRONICS

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µPSD325X DEVICES

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Programming Flash Memory

Flash memory must be erased prior to being pro-

grammed. A byte of Flash memory is erased to all

’1s’ (FFh), and is programmed by setting selected

bits to ’0.’ The MCU may erase Flash memory all

at once or by-sector, but not byte-by-byte. Howev-

er, the MCU may program Flash memory byte-by-

byte.

The primary and secondary Flash memories re-

quire the MCU to send an instruction to program a

byte or to erase sectors (see Table 85).

Once the MCU issues a Flash memory Program or

Erase instruction, it must check for the status bits

for completion. The embedded algorithms that are

invoked support several means to provide status

to the MCU. Status may be checked using any of

three methods: Data Polling, Data Toggle, or

Ready/Busy (PC3).

Data Polling. Polling on the Data Polling Flag Bit

(DQ7) is a method of checking whether a Program

or Erase cycle is in progress or has completed.

Figure 52 shows the Data Polling 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 Data Polling Flag Bit

(DQ7) of this location becomes the complement of

b7 of the original data byte to be programmed. The

MCU continues to poll this location, comparing the

Data Polling Flag Bit (DQ7) and monitoring the Er-

ror Flag Bit (DQ5). When the Data Polling Flag Bit

(DQ7) matches b7 of the original data, and the Er-

ror Flag Bit (DQ5) remains ’0,’ the embedded algo-

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

the MCU should test the Data Polling Flag Bit

(DQ7) again since the Data Polling Flag Bit (DQ7)

may have changed simultaneously with the Error

Flag Bit (DQ5) (see Figure 52).

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 the Flash memory with the

byte that was intended to be written.

When using the Data Polling method during an

Erase cycle, Figure 52 still applies. However, the

Data Polling Flag Bit (DQ7) is ’0’ until the Erase cy-

cle is complete. A ’1’ on the Error Flag Bit (DQ5) in-

dicates a time-out condition on the Erase cycle; a

’0’ indicates no error. The MCU can read any loca-

tion within the sector being erased to get the Data

Polling Flag Bit (DQ7) and the Error Flag Bit

(DQ5).

PSDsoft Express generates ANSI C code func-

tions which implement these Data Polling algo-

rithms.

Figure 52. Data Polling Flowchart

READ DQ5 & DQ7

at VALID ADDRESS

START

READ DQ7

FAIL

PASS

AI01369B

DQ7

DATA

YES

DQ5

= 1

DQ7

DATA

YES

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