9202 datasheet(117/175 Pages) STMICROELECTRONICS

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UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV

Separate Space Mode. Program space is sepa-

rated from Data space. For example, Program Se-

lect Enable (PSEN) is used to access the program

code from the primary Flash memory, while READ

Strobe (RD) is used to access data from the sec-

ondary Flash memory, SRAM and I/O Port blocks.

This configuration requires the VM Register to be

set to 0Ch (see Figure 55).

Combined Space Modes. The

Program

and

Data spaces are combined into one memory

space that allows the primary Flash memory, sec-

ondary Flash memory, and SRAM to be accessed

by either Program Select Enable (PSEN) or READ

Strobe (RD). For example, to configure the prima-

ry Flash memory in Combined space, Bits b2 and

b4 of the VM Register are set to '1' (see Figure 56).

Figure 55. Separate Space Mode

Figure 56. Combined Space Mode

Primary

Flash

Memory

DPLD

Secondary

Flash

Memory

SRAM

RS0

CSBOOT0-3

FS0-FS7

PSEN

AI02869C

Primary

Flash

Memory

DPLD

Secondary

Flash

Memory

SRAM

RS0

CSBOOT0-3

FS0-FS7

VM REG BIT 2

PSEN

VM REG BIT 0

VM REG BIT 1

VM REG BIT 3

VM REG BIT 4

AI02870C

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