PSD913F2 datasheet(25/94 Pages) STMICROELECTRONICS

25 / 94 page

Preliminary Information

PSD9XX Family

9.1.1.6 Programming Flash Memory

Flash memory must be erased prior to being programmed. 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. Although erasing Flash

memory occurs on a sector basis, programming Flash memory occurs on a byte basis.

The PSD9XX main Flash and Secondary Flash memories require the MCU to send an

instruction to program a byte or perform an erase function (see Table 9).

Once the MCU issues a Flash memory program or erase instruction, it must check for the

status of completion. The embedded algorithms that are invoked inside the PSD9XX

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.

9.1.1.6.1 Data Polling

Polling on DQ7 is a method of checking whether a Program or Erase instruction is in

progress or has completed. Figure 3 shows the Data Polling algorithm.

When the MCU issues a programming instruction, the embedded algorithm within the

PSD9XX 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 programmed. 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

simultaneously with DQ5 (see Figure 3).

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 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 with

the byte that was intended to be written.

When using the Data Polling method after an erase instruction, Figure 3 still applies.

However, DQ7 will be ‘0’ until the erase operation is complete. 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 will generate ANSI C code functions which implement these Data Polling

algorithms.

The

PSD9XX

Functional

Blocks

(cont.)

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