ST6369 datasheet(16/71 Pages) STMICROELECTRONICS

16 / 71 page

MEMORY SPACES (Continued)

Data ROM Addressing. All the read-only data are

physically implemented in the ROM in which the

Program Space is also implemented. The ROM

therefore contains the program to be executed and

also the constants and the look-up tables needed

for the program. The locations of Data Space in

which the different constants and look-up tables

are addressed by the ST6369 Core can be consid-

ered as being a 64-byte window through which it is

possible to access to the read-only data stored in

the ROM. This window is located from the 40H ad-

dress to the 7FH address in the Data space and al-

lows the direct reading of the bytes from the 000H

address to the 03FH address in the ROM. All the

bytes of the ROM can be used to store either in-

structions or read-only data. Indeed, the window

can be moved by step of 64 bytes along the ROM

in writing the appropriate code in the Write-only

Data ROM Window register (DRWR, location

C9H). The effective address of the byte to be read

as a data in the ROM is obtained by the concatena-

tion of the 6 less significant bits of the address in

the Data Space (as less significant bits) and the

content of the DRWR (as most significant bits). So

when addressing location 40H of data space, and

0 is loaded in the DRWR, the physical addressed

location in ROM is 00H.

DWR6-DWR0. These are the Data Rom Window

bits that correspond to the upper bits of data ROM

program space. This register is undefined after re-

set.

Note. Care is required when handling the DRWR as

it is write only. For this reason, it is not allowed to

change the DRWR contents while executing inter-

rupts drivers, as the driver cannot save and than re-

store its previous content. If it is impossible to avoid

the writing of this register in interrupts drivers, an im-

age of this register must be saved in a RAM location,

and each time the program writes the DRWR it

writes also the image register. The image register

must be written first, so if an interrupt occurs be-

tween the two instructions the DRWR register is not

affected.

DWR

Data ROM Window Register

(C9H, Write Only)

D7 D6 D5 D4 D3 D2 D1 D0

DWR0 = Data ROM Window 0

DWR1 = Data ROM Window 1

DWR2 = Data ROM Window 2

DWR3 = Data ROM Window 3

DWR4 = Data ROM Window 4

DWR5 = Data ROM Window 5

DWR6 = Data ROM Window 6

UNUSED

Figure 14. Data ROM Window Register

DATA ROM

WINDOW REGISTER

CONTENTS

DATA SPACE ADDRESS

40h-7Fh

IN INSTRUCTION

PROGRAM SPACE ADDRESS

65432

543

210

543

210

READ

VR01573B

DATA SPACE ADDRESS

59h

Example:

(DWR)

DWR=28h

ROM

ADDRESS:A19h

Figure 15. Data ROM Window Memory Addressing

ST6369

12/67

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