Specifications

Chapter 3 - Instruction Set

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CHAPTER 3

Instruction Set

Introduction

Instruction set in PIC16Cxx microcontroller family

Data Transfer

Arithmetic and logic

Bit operations

Directing the program flow

Instruction execution period

Word list

Introduction

We have already mentioned that microcontroller is not like any other integrated circuit. When they

come out of production most integrated circuits are ready to be built into devices which is not the

case with microcontrollers. In order to "make" microcontroller perform a task, we have to tell it

exactly what to do, or in other words we must write the program microcontroller will execute. We

will describe in this chapter instructions which make up the assembler, or lower-level program

language for PIC microcontrollers.

Instruction Set in PIC16Cxx Microcontroller Family

Complete set which includes 35 instructions is given in the following table. A reason for such a small

number of instructions lies primarily in the fact that we are talking about a RISC microcontroller

whose instructions are well optimized considering the speed of work, architectural simplicity and

code compactness. The only drawback is that programmer is expected to master "uncomfortable"

technique of using a reducedt set of 35 instructions.

Data transfer

Transfer of data in a microcontroller is done between work (W) register and an 'f' register that

represents any location in internal RAM (regardless whether those are special or general purpose

registers).

First three instructions (look at the following table) provide for a constant being written in W register

(MOVLW is short for MOVe Literal to W), and for data to be copied from W register onto RAM and

data from RAM to be copied onto W register (or on the same RAM location, at which point only the

status of Z flag changes). Instruction CLRF writes constant 0 in 'f ' register, and CLRW writes

constant 0 in register W. SWAPF instruction exchanges places of the 4-bit nibbles field inside a

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