ST6373 datasheet(9/64 Pages) STMICROELECTRONICS

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ST6373

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MEMORY SPACES (Cont’d)

Program ROM Page Register (PRPR)

Address: CAh - Write only

Reset Value: XXh

D7-D3. These bits are not used but have to be

written to “0”.

PRPR2-PRPR0. These are the program ROM

banking bits and the value loaded selects the cor-

responding page to be addressed in the lower part

of 4K program address space as specified in Table

3.This register is undefined on reset.

Note:

Only the lower part of address space has been

bankswitched because interrupt vectors and com-

mon subroutines should be available all the time.

The reason of this structure is due to the fact that it

is not possible to jump from a dynamic page to an-

other, unless jumping back to the static page,

changing contents of PRPR, and, then, jumping to

a different dynamic page.

Care is required when handling the PRPR as it is

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

change the PRPR contents while executing inter-

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

store its previous content. Anyway, this operation

may be necessary if the sum of common routines

and interrupt drivers will take more than 2K bytes;

in this case could be necessary to divide the inter-

rupt driver in a (minor) part in the static page (start

and end), and in the second (major) part in one dy-

namic page. If it is impossible to avoid the writing of

this register in interrupts drivers, an image of this

time the program writes the PRPR bit writes also

the image register. The image register must be

written first, so if an interrupt occurs between the

two instructions the PRPR is not affected.

Table 3. Program Memory Page Register Coding

Table 4. ST6373 Program Memory Map

Note *): all reserved areas must be set to FFh in the ROM code.

PRPR2 PRPR1 PRPR0

PRPR2 PRPR1 PRPR0 PC11

Memory Page

Static Page (Page 1)

000

Page 0

Page 1 (Static Page)

010

Page 2

011

Page 3

100

Page 4

101

Page 5

110

Page 6

111

Page 7

Program Memory Page

Device Address

Description*)

PAGE 0

0000h-007Fh

0080h-07FFh

Reserved

User ROM

PAGE 1

“STATIC”

0800h-0F9Fh

0FA0h-0FEFh

0FF0h-0FF7h

0FF8h-0FFBh

0FFCh-0FFDh

0FFEh-0FFFh

User ROM

Reserved

Interrupt Vectors

Reserved

NMI Vector

Reset Vector

PAGE 2

0000h-000Fh

0010h-07FFh

Reserved

User ROM

PAGE 3

0000h-000Fh

0010h-07FFh

Reserved

User ROM (End of 8K)

PAGE 4

0000h-000Fh

0010h-07FFh

Reserved

User ROM

PAGE 5

0000h-000Fh

0010h-07FFh

Reserved

User ROM (End of 12K)

PAGE 6

0000h-000Fh

0010h-07FFh

Reserved

User ROM

PAGE 7

0000h-000Fh

0010h-07FFh

Reserved

User ROM (End of 16K)

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