PSD413A2 datasheet(65/123 Pages) STMICROELECTRONICS

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PSD4XX Family

9.4.4 Memory Select Map For 8031 Application

The 8031 family of microcontrollers has separate code memory space and data memory

space. This feature requires a different Memory Select Map. Two modes of operation are

provided for 8031 applications. The selection of the modes is specified in the PSD4XX

PSDsoft Software (PSDconfiguration):

t Separate Space Mode

In this mode, the PSEN signal is used to access code from EPROM, and the RD

signal is used to access data from SRAM. The code memory space is separated from

the data memory space.

t Combined Space Mode

In this mode, the EPROM can be accessed by PSEN or RD. The EPROM is used for

code and data storage. The memory block's address space cannot overlap.

If data and code memory blocks must overlap each other, the RD signal can be included as

an additional address input in generating the EPROM chip select signals (ES0 – ES3). In

this case the EPROM access time is from the RD valid to data valid. Figures 32a and 32b

show the memory configuration in the two modes.

In some applications it is desirable to execute program codes in SRAM. The PSD4XX

provides this option by enabling PSEN to access SRAM. To activate this option, the

SRCODE bit of the VM Register must be set to “1” (see Table 17). SRAM space can

overlap EPROM space and has priority when PSEN is used.

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

***

SRCODE

PIO

1 = ON

* = Reserved for future use, bits set to zero.

Table 17. VM Register

The PSD4XX

Architecture

(cont.)

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