ST63142 datasheet(14/86 Pages) STMICROELECTRONICS

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PROGRAM SPACE

VR001568

INTERRUPT &

RESET VEC TOR S

AC CUMUL ATOR

WREGISTER

RA M

DATA ROM

WINDOW

RAM / EEPROM

BANKING AR EA

DATA SPACE

DATA RAM

BANK S ELECT

DATA ROM

WIND OW SELECT

VREGISTER

YREGISTER

XREGISTER

0-63

0000h

07FFh

0800h

0FF0h

0FFFh

000h

03Fh

040h

070h

080h

081h

082h

083h

084h

0FFh

0C 0h

ROM

STACK LEVEL 1

STACK LEVEL 2

STACK LEVEL 3

STACK LEVEL 4

STACK LEVEL 5

STACK LEVEL 6

PROGRAM COUNTER

STAC K SPAC E

Figure 7. ST631xx Memory Addressing Description Diagram

MEMORY SPACES

The MCUs operate in three different memory

spaces: Program Space, Data Space, and Stack

Space. A description of these spaces is shown in

the following Figures.

Program Space

The program space is physically implemented in

the ROM and includes all the instructions that are

to be executed, as well as the data required for the

immediate addressing mode instructions, the re-

served test area and user vectors. It is addressed

thanks to the 12-bit Program Counter register (PC

dress up to 4K bytes of Program Space. Neverthe-

less, the Program Space can be extended by the

addition of 2-Kbyte ROM banks as it is shown in

Figure 8 in which the 8K bytes memory is de-

scribed.

These banks are addressed by pointing to the

000h-7FFh locations of the Program Space thanks

to the Program Counter, and by writing the appro-

priate code in the Program ROM Page Register

(PRPR) located at address CAh

of the Data

Space. Because interrupts and common subrou-

tines should be available all the time only the lower

2K bytes of the 4K program space are bank

switched while the upper 2K bytes can be seen as

Program

counter

space

0000h

1FFFh

0FFFh

Static Page

Page 1

0800h

07FFh

Page 0

Page 1

Static Page

Page 2

Page 3

0000h

Figure 8. ST631xx 8K Bytes Program Space

Addressing Description

static space. Table 3 gives the codes that allow the

selection of the corresponding banks.

Note that, from the memory point of view, the Page

1 and the Static Page represent the same physical

memory: it is only a different way of addressing the

same location. On the ST631xx a total of 8192

bytes of ROM have been implemented; 7948 are

available as user ROM while 244 are reserved for

testing.

ST63140,142,126,156

10/82

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