Instructions

Overview

An instruction can be split into 2 parts, the command to use and the data to use for the command.

https://www.youtube.com/watch?v=2h3hQCV3YcE&index=117&list=PLCiOXwirraUDUYF_qDYcZV8Hce8dsE_Ho

OpCode

The command for the instruction, ie Load, Store, Add

Operand

The data to be used by the OpCode, this can be data eg #21 (ie the number 21) or it can be an address eg 21 (ie memory location 21)

Addressing

https://www.youtube.com/watch?v=yKNrFfVdu3g&list=PLCiOXwirraUDUYF_qDYcZV8Hce8dsE_Ho&index=120

Immediate Addressing

The operand is data eg #21

Direct Addressing

The operand is a location eg 21

Indirect Addressing - not in AQA Specification

The operand is a location which contains the location for the instruction

Index Addressing - not in AQA Specification

The operand is the number in the Index Regisiter after the location in the instruction