PSD913F2 datasheet(20/94 Pages) STMICROELECTRONICS

20 / 94 page

PSD9XX Family

Preliminary Information

9.1.1.1 Memory Block Selects

The decode PLD in the PSD9XX generates the chip selects for all the internal memory

blocks (refer to the PLD section). Each of the eight Flash memory sectors have a

Flash Select signal (FS0-FS7) which can contain up to three product terms. Each of the

four secondary Flash memory sectors have a Select signal (CSBOOT0-3) which can

contain up to three product terms. Having three product terms for each sector select signal

allows a given sector to be mapped in different areas of system memory. When using a

microcontroller with separate Program and Data space, these flexible select signals allow

dynamic re-mapping of sectors from one space to the other when used with the VM

9.1.1.2 The Ready/Busy Pin (PC3)

Pin PC3 can be used to output the Ready/Busy status of the PSD9XX. The output on the

pin will be a ‘0’ (Busy) when Flash memory blocks are being written to, or when the Flash

memory block is being erased. The output will be a ‘1’ (Ready) when no write or erase

operation is in progress.

9.1.1.3 Memory Operation

The main Flash and secondary Flash memories are addressed through the microcontroller

interface on the PSD9XX device. The microcontroller can access these memories in one of

two ways:

t The microcontroller can execute a typical bus write or read operation just as it would

if accessing a RAM or ROM device using standard bus cycles.

t The microcontroller can execute a specific instruction that consists of several write

and read operations. This involves writing specific data patterns to special addresses

within the Flash to invoke an embedded algorithm. These instructions are summarized

in Table 9.

Typically, Flash memory can be read by the microcontroller using read operations, just

as it would read a ROM device. However, Flash memory can only be erased and

programmed with specific instructions. For example, the microcontroller cannot write a

single byte directly to Flash memory as one would write a byte to RAM. To program a byte

into Flash memory, the microcontroller must execute a program instruction sequence, then

test the status of the programming event. This status test is achieved by a read operation

or polling the Rdy/Busy pin (PC3).

The Flash memory can also be read by using special instructions to retrieve particular

Flash device information (sector protect status and ID).

The

PSD9XX

Functional

Blocks

(cont.)

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