UPSD325X datasheet(107/176 Pages) STMICROELECTRONICS

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µPSD325X DEVICES

PSD MODULE DETAILED OPERATION

As shown in Figure 15, the PSD MODULE con-

sists of five major types of functional blocks:

Memory Block

PLD Blocks

I/O Ports

Power Management Unit (PMU)

JTAG Interface

The functions of each block are described in the

following sections. Many of the blocks perform

multiple functions, and are user configurable.

MEMORY BLOCKS

The PSD MODULE has the following memory

blocks:

– Primary Flash memory

– Secondary Flash memory

–SRAM

The Memory Select signals for these blocks origi-

nate from the Decode PLD (DPLD) and are user-

defined in PSDsoft Express.

Primary Flash Memory and Secondary Flash

memory Description

The primary Flash memory is divided evenly into

eight equal sectors. The secondary Flash memory

is divided into four equal sectors. Each sector of

either memory block can be separately protected

from Program and Erase cycles.

Flash memory may be erased on a sector-by-sec-

tor basis. Flash sector erasure may be suspended

while data is read from other sectors of the block

and then resumed after reading.

During a Program or Erase cycle in Flash memory,

the status can be output on Ready/Busy (PC3).

This pin is set up using PSDsoft Express Configu-

ration.

Memory Block Select Signals

The DPLD generates the Select signals for all the

internal memory blocks (see the section entitled

“PLDs,” page 120). Each of the eight sectors of the

primary Flash memory has a Select signal (FS0-

FS7) which can contain up to three product terms.

Each of the four sectors of the secondary Flash

memory

has

Select

signal

(CSBOOT0-

CSBOOT3) which can contain up to three product

terms. Having three product terms for each Select

signal allows a given sector to be mapped in Pro-

gram or Data space.

Ready/Busy (PC3). This signal can be used to

output the Ready/Busy status of the Flash memo-

ry. The output on Ready/Busy (PC3) is a '0' (Busy)

when Flash memory is being written to,

or when

Flash memory is being erased. The output is a 1

(Ready) when no WRITE or Erase cycle is in

progress.

Memory Operation. The primary Flash memory

and secondary Flash memory are addressed

through the MCU Bus. The MCU can access these

memories in one of two ways:

The MCU can execute a typical bus WRITE or

READ

operation.

The MCU can execute a specific Flash memory

instruction that consists of several WRITE and

READ operations. This involves writing specific

data patterns to special addresses within the

Flash memory to invoke an embedded

algorithm. These instructions are summarized

in Table 85.

Typically, the MCU can read Flash memory using

READ operations, just as it would read a ROM de-

vice. However, Flash memory can only be altered

using specific Erase and Program instructions. For

example, the MCU cannot write a single byte di-

rectly to Flash memory as it would write a byte to

RAM. To program a byte into Flash memory, the

MCU must execute a Program instruction, then

test the status of the Program cycle. This status

test is achieved by a READ operation or polling

Ready/Busy (PC3).

Flash memory can also be read by using special

instructions to retrieve particular Flash device in-

formation (sector protect status and ID).

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