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PSD813F1-A

Flash In-System Programmable (ISP) Peripherals For 8-bit MCUs

STMicroelectronics 

PSD813F1-A

The

PSD813F1

Functional

Blocks

(cont.)

Preliminary

9.1.1.1 Memory Block Selects

The decode PLD in the PSD813F1 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 EEPROM memory sectors have a Select signal (EES0-3 or 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.

9.1.1.2 The Ready/Busy Pin (PC3)

Pin PC3 can be used to output the Ready/Busy status of the PSD813F1. The output on

the pin will be a ‘0’ (Busy) when Flash or EEPROM 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 EEPROM memory are addressed through the microcontroller interface

on the PSD813F1 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 or EEPROM 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 EEPROM is a bit different. Data can be written to EEPROM memory using write

operations, like writing to a RAM device, but the status of each write event must be checked

by the microcontroller. A write event can be one to 64 contiguous bytes. The status test is

very similar to that used for Flash memory (read operation or Rdy/Busy). Optionally, the

EEPROM memory may be put into a Software Data Protect (SDP) mode where it requires

instructions, rather than operations, to alter its contents. SDP mode makes writing to

EEPROM much like writing to Flash memory.

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