PSD813F1 datasheet(27/110 Pages) STMICROELECTRONICS

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PSD813F1

PROGRAMMING FLASH MEMORY

Flash memory must be erased prior to being pro-

grammed. The MCU may erase Flash memory all

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

of Flash memory erases to all logic ones (FF hex),

and its bits are programmed to logic zeros. Al-

though erasing Flash memory occurs on a sector

basis, programming Flash memory occurs on a

byte basis.

The PSD main Flash and optional boot Flash re-

quire the MCU to send an instruction to program a

byte or perform an erase function (see Table

8., page 20). This differs from EEPROM, which

can be programmed with simple MCU bus write

operations (unless EEPROM SDP mode is en-

abled).

Once the MCU issues a Flash memory program or

erase instruction, it must check for the status of

completion. The embedded algorithms that are in-

voked inside the PSD support several means to

provide status to the MCU. Status may be checked

using any of three methods: Data Polling, Data

Toggle, or the Ready/Busy output pin.

Data Polling

Polling on DQ7 is a method of checking whether a

Program or Erase instruction is in progress or has

completed. Figure 9 shows the Data Polling algo-

rithm.

When the MCU issues a programming instruction,

the embedded algorithm within the PSD begins.

The MCU then reads the location of the byte to be

programmed in Flash to check status. Data bit

DQ7 of this location becomes the compliment of

data bit 7of the original data byte to be pro-

grammed. The MCU continues to poll this location,

comparing DQ7 and monitoring the Error bit on

DQ5. When the DQ7 matches data bit 7 of the

original data, and the Error bit at DQ5 remains ‘0’,

then the embedded algorithm is complete. If the

Error bit at DQ5 is ‘1’, the MCU should test DQ7

again since DQ7 may have changed simulta-

neously with DQ5 (see Figure 9).

The Error bit at DQ5 will be set if either an internal

timeout 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 with the byte that was in-

tended to be written.

When using the Data Polling method after an

erase instruction, Figure 9 still applies. However,

DQ7 will be ‘0’ until the erase operation is com-

plete. A ‘1’ on DQ5 will indicate a timeout failure of

the erase operation, a ‘0’ indicates no error. The

MCU can read any location within the sector being

erased to get DQ7 and DQ5.

PSDsoft Express will generate ANSI C code func-

tions which implement these Data Polling algo-

rithms.

Figure 9. 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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