PSD834210MIT datasheet(15/89 Pages) STMICROELECTRONICS

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PSD834F2V

DETAILED OPERATION

As shown in Figure 2, the PSD consists of six ma-

jor types of functional blocks:

Memory Blocks

PLD Blocks

MCU Bus Interface

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 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”, on page 27). 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 a 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 differ-

ent areas of system memory. When using a MCU

with separate Program and Data space, these

flexible Select signals allow dynamic re-mapping

of sectors from one memory space to the other.

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

output the Ready/Busy status of the PSD. The out-

put 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 Interface. The MCU can ac-

cess these memories in one of two ways:

The MCU can execute a typical bus Write or

Read

operation just as it would if accessing a

RAM or ROM device using standard bus cycles.

The MCU 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 memory to

invoke an embedded algorithm. These

instructions are summarized in Table 7.

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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