ST9 datasheet(21/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

As an example, if RP0 is set to half group 2 (lower part of whole group 1) and RP1 to half

group 27 (upper part of whole group 13), r0 will designate R16 (2 x 8 + 0) while r15 designates

R223 (27 x 8 + 7).

Using either method depends on the organization of the data in the register file. You may find

it convenient to use two 8-register blocks if you need to make quick calculations on pairs of

data that are far apart in the register file.

The page numbering and switching instructions are summarized below:

Table 2.

When you use an 8- or 16-register group, you may very likely have a subroutine or an interrupt

routine that uses a different set of working registers. You must save (push) the pair of register

pointers RPP that include RP0 and RP1 at the beginning of the routine and restore them on

exit.

3.1.6.3 Peripheral Register Paging

Group F of the 16-register groups is paged so that as many as 64 different groups can be

mapped to this address range. This large space is used to accommodate the registers related

to the peripherals. The paging technique allows you to add any number of peripherals and still

be able to handle them without using up more addresses in the register space.

When you access a register in group 15, first set the Page Pointer Register to the number of

the page that contains the register you want. Here is how a page is selected:

Hexa-

decimal

number

Decimal

number

Function

Eight-Register

block decimal

(hexadecimal)

srp0 #n (or srp1) #n

instructions to select a block to

provide r0-r7

and r8-r15 respectively

F8-FF

248-255

Paged registers

31 (1F)

srp0 or srp1 #31

F0-F7

240-247

Paged registers

30 (1E)

srp0 or srp1 #30

E8-EF

232-239

System registers

29 (1D)

srp0 or srp1 #29

E0-E7

224-231

System registers

28 (1C)

srp0 or srp1 #28

D8-DF

216-223

General

purpose

registers

27 (1B)

srp0 or srp1 #27

D0-D7

208-215

26 (1A)

srp0 or srp1 #26

C8-CF

200-207

25 (19)

srp0 or srp1 #25

...

78-7F

120-127

15 (0F)

srp0 or srp1 #15

...

20-27

32-39

srp0 or srp1 #4

18-1F

24-31

srp0 or srp1 #3

10-17

16-23

srp0 or srp1 #2

08-0F

08-15

srp0 or srp1 #1

00-07

srp0 or srp1 #0

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