ST9291 datasheet(7/20 Pages) STMICROELECTRONICS

7 / 20 page

64K

PROGRAM

MEMORY

FILE

64K

DATA

MEMORY

VA00430

Figure 1-4. Address Spaces

1 CORE DESCRIPTION

1.1 CORE ARCHITECTURE

1.1.1 INTRODUCTION

The Core or Central Processing Unit (CPU) of the

ST9 includes the 8 bit Arithmetic Logic Unit and the

16 bit Program Counter, System and User Stack

Pointers. The microcoded Instruction Set is highly

optimised for both byte (8 bit) and word (16 bit)

data, BCD and Boolean data types, with 14 ad-

dressing modes.

Three independent buses are controlled by the

Core, a 16 bit Memory bus, an 8 bit Register ad-

dressing bus and a 6 bit Interrupt/DMA bus con-

nected to the interrupt and DMA controllers in the

on-chip peripherals and the Core. This multiple bus

architecture allows a high degree of pipelining and

parallel operation, giving the ST9 its efficiency in

both numerical calculations and communication

with the on-chip peripherals.

1.1.2 ADDRESS SPACES

The ST9 has three separate address spaces:

- Register File: 240 8-bit registers plus up to 64

pages of 16 bytes each, located in the on-chip

peripherals.

- Data memory with up to 64K (65536) bytes

- Program memory with up to 64K (65536) bytes

The Data and Program memory spaces will be ad-

dressed in further detail in section 1.3.

1.1.2.1 Register File

The Register File consists of:

- 224 general purpose registers R0 to R223

- 16 system registers in the System Group

(R224 to R239).

- I/O pages depending on the configuration of

the ST9, each containing up to 16 registers,

with paging facilities based on the top group

(R240 to R255).

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