ST6380 datasheet(9/82 Pages) STMICROELECTRONICS

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ST6380, ST6381, ST6382, ST6383, ST6388, ST6389

1.3 MEMORY SPACES

The MCU operates in three different memory

spaces: Stack Space, Program Space and Data

Space.

1.3.1 Stack Space

The stack space consists of six 12 bit registers that

are used for stacking subroutine and interrupt re-

turn addresses plus the current program counter

1.3.2 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 the user vectors. It is ad-

dressed thanks to the 12-bit Program Counter reg-

ister (PC register) and the ST6 Core can directly

address up to 4K bytes of Program Space. Never-

theless, the Program Space can be extended by

the addition of 2Kbyte memory banks as it is

shown in Figure 5, in which the 20K bytes memory

is described. These banks are addressed by point-

ing to the 000h-7FFh locations of the Program

Space thanks to the Program Counter, and by writ-

ing the appropriate code in the Program ROM

Page Register (PRPR) located at address CAh in

the Data Space. Because interrupts and common

subroutines should be available all the time only

the lower 2K byte of the 4K program space are

bank switched while the upper 2K byte can be

seen as static space. Table 3 gives the different

codes that allows the selection of the correspond-

ing 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

ST6388 and ST6389, a total of 20480 bytes of

ROM have been implemented; 20140 bytes are

available as User ROM while 340 bytes are re-

served for testing.

Figure 4. 20K-Byte Program Space Addressing

Figure 5. Memory Addressing Diagram

Program

counter

space

0FFFh

0800h

07FFh

0000h

Static

Page

Page 1

Page 0

4FFFh

Page 1

Page 9

Static Page

...

PROGRAM SPACE

ROM

INTERRUPT &

RESET VECTORS

ACCUMULATOR

DATA RAM

BANK SELECT

DATA ROM

WINDOW SELECT

RAM

X REGISTER

Y REGISTER

V REGISTER

W REGISTER

DATA ROM

WINDOW

RAM / EEPROM

BANKING AREA

000h

03Fh

040h

07Fh

080h

081h

082h

083h

084h

0C0h

0FFh

0-63

DATA SPACE

0000h

0FF0h

0FFFh

PROGRAM COUNTER

STACK LEVEL 1

STACK LEVEL 2

STACK LEVEL 3

STACK LEVEL 4

STACK LEVEL 5

STACK LEVEL 6

vr01568

STACK SPACE

ROM

07FFh

0800h

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