ST9291 datasheet(9/20 Pages) STMICROELECTRONICS

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1.1.2.2 Addressing Registers

All registers in the Register File and pages can be

specified by using a decimal, hex or binary ad-

dress, e.g. R231, RE7h or R11100111b is the

same register.

The registers can be referred to by their hexadeci-

mal group address, so that registers R0-R15 form

group 0, R160-R175 form group A and so on.

Working Register Addresses

The 8-bit register address is formed by 2 nibbles,

for example, for register R195 or RC3h or

R11000011, 1100 specifies the 13th group (i.e.

group C) and 0011 specifies the 3rd register in that

group.

Working registers are addressed by supplying the

least significant nibble in the instruction and adding

it to the most significant nibble found in the Regis-

ter Pointer (R233). Working register addressing is

shown in Figure 1-7.

System Registers

The 16 system registers at addresses R224 to

R239 form Group E.

The system registers are addressable using any of

the 4 register addressing modes and the most sig-

nificant nibble will, in all cases, be 14 (0Eh).

Paged Registers

There are a maximum of 64 pages each containing

16 registers. These are addressed using the regis-

ter addressing modes with the addition of the Page

Pointer register, R234. This register selects the

page to be addressed in group F and once set,

does not need to be changed if two or more regis-

ters on the same page are to be addressed in suc-

cession.

Therefore if the Page Pointer, R234, is set to 5, the

instructions

spp 5

ld R242, r4

will load the contents of working register r4 into the

third register (R242) of page 5.

These paged registers hold data and control regis-

ters related to the on-chip peripherals, and thus the

configuration depends upon the peripheral organi-

sation of each ST9 family member. i.e. pages only

exist if the peripheral exists.

Available pages are shown in Table 1-3.

1.1.2.3 Input/Output Ports

The Input/Output ports are located in two areas.

The port registers for Ports 0-5 are located at the

bottom of the System register group in locations

R224 to R229.

Each Port has three associated Control registers,

which determine the individual pin modes (I/O,

Open-Drain etc). These registers are located in

pages 2 and 3.

ADDRESS SPACES (Continued)

Hex.

Address

Decimal

Address

Function

Group

F0-FF

240-255

Paged

Registers

Group F

E0-EF

224-239

System

Registers

Group E

D0-DF

208-223

General

Purpose

Registers

Group D

C0-CF

192-207

Group C

B0-BF

176-191

Group B

A0-AF

160-175

Group A

90-9F

144-159

Group 9

80-8F

128-143

Group 8

70-7F

112-127

Group 7

60-6F

96-111

Group 6

50-5F

80-95

Group 5

40-4F

64-79

Group 4

30-3F

48-63

Group 3

20-2F

32-47

Group 2

10-1F

16-31

Group 1

00-0F

00-15

Group 0

Table 1-2. Register File Organization

ST9291

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