ST72321R6-Auto datasheet(33/243 Pages) STMICROELECTRONICS

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ST72321xx-Auto

Central processing unit (CPU)

Doc ID 13829 Rev 1

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Central processing unit (CPU)

5.1

Introduction

This CPU has a full 8-bit architecture and contains six internal registers allowing efficient 8-

bit data manipulation.

5.2

Main features

●

Enable executing 63 basic instructions

●

Fast 8-bit by 8-bit multiply

●

17 main addressing modes (with indirect addressing mode)

●

Two 8-bit index registers

●

16-bit stack pointer

●

Low power Halt and Wait modes

●

Priority maskable hardware interrupts

●

Non-maskable software/hardware interrupts

5.3

CPU registers

The six CPU registers shown in Figure 7 are not present in the memory mapping and are

accessed by specific instructions.

Figure 7.

CPU registers

Accumulator

X index register

Y index register

Stack pointer

Condition code register

Program counter

1I1 H I0 N Z

Reset value = reset vector @ FFFEh-FFFFh

PCH

PCL

8 7

Reset value = stack higher address

Reset value = 1

11 X 1 X X

Reset value = XXh

X = undefined value

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