Instruction set refers to the set of Instruction that a computer can perform. As depicted in the above picture Instruction Set is specified by the software and has to be implemented by the hardware. More number of instructions implies greater complexity for the hardware.
Before we jump in the making we need to make sure about the number and type of instructions that are to be used in our computer. In this project we will use three types of instructions. Namely: MRI, RRI and IO.
- Memory Reference Instruction ( MRI )
- These are instruction that performs operations which involve the memory. Write/Read operations to and from Memory is a common phenomena.
- In this project we will be using seven MRIs. These are:
- AND
- ADD
- LDA ( Load Accumulator )
- STA ( Store Accumulator )
- BUN ( Branch Unconditionally )
- BSA ( Branch and Save Return Address )
- ISZ ( Increment and Skip if Zero )
- Register Reference Instruction ( RRI )
- These instruction operates on different registers used in the computer. There are various registers that we will discuss in later section.
- We will use four RRIs in our project. These are:
- CLA ( Clear Accumulator )
- CLE ( Clear E )
- CMA ( Compliment Accumulator )
- HLT ( Halt Computer )
- Input/Output
- These instruction deal with input and output devices. For example, taking input from an input device and displaying the data through an output device involves Input/Output operations.
- We will use four IO in our project. These are:
- INP ( Input Character )
- OUT (Ouput Character )
- SKI ( Skip on input flag )
- SKO (Skip on output flag )
There are altogether 15 (7 + 4 + 4 ) instruction that we will use in our computer. At first these instruction may not give you a clear picture of what a real computer is. As we go further topic by topic things will be more clear.
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