Central Processing Unit; Introduction; Main Features; Cpu Registers - STMicroelectronics ST72361 Auto Series Manual

Central processing unit

4 Central processing unit
4.1

Introduction

This CPU has a full 8-bit architecture and contains six internal registers allowing efficient
8-bit data manipulation.
4.2

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
4.3

CPU registers

The six CPU registers shown in
accessed by specific instructions.
4.3.1

Accumulator (A)

The Accumulator is an 8-bit general purpose register used to hold operands and the results
of the arithmetic and logic calculations and to manipulate data.
4.3.2

Index registers (X and Y)

These 8-bit registers are used to create effective addresses or as temporary storage areas
for data manipulation. (The Cross-Assembler generates a precede instruction (PRE) to
indicate that the following instruction refers to the Y register.)
The Y register is not affected by the interrupt automatic procedures.
4.3.3

Program counter (PC)

The program counter is a 16-bit register containing the address of the next instruction to be
executed by the CPU. It is made of two 8-bit registers PCL (Program Counter Low which is
the LSB) and PCH (Program Counter High which is the MSB).
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Figure 8 are not present in the memory mapping and are
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