simpletron

This is my implementation of the simpletron computer from the book C How to Program.

Simpletron is a simulated computer that that can be programmed using the Simpletron Machine Language(SML). The Simpletron Machine language contains 12 instructions. The length of each instruction is four numerical values which is refered to as a word.

1009     // Read a value from the keyboard and store it into memory address 09                                                                                                                        
1010     // Read a value from the keyboard and store it into memory address 10                                                   
2009     // load the value from memory address 09 into the accumulator                                                   
3010     // Add the value from memory address 10 to the accumulator                                                                                                                        
2111     // Store the value from the accumulator into memory address 11                                                              
1111     // Write the value from memory address 11 to the terminal                                                                                                                        
4300     // Halt the program

The program above is SML, it instructs the computer to add two numbers together.

Usage

To use the C implementation of Simpletron, follow the instruction below:

cd c-simpletron
gcc main.c -o main # compile the program
./main # run the program

You are going to add your instructions one line at a time and press enter. To end the instruction entering phase provide the value -9999.

Memory

The simpletron can only store 100 words in memory. The memory location ranges from 00 to 99.

Registers

The simpletron has 3 registers, 1 is a general purpose register the other two are special purpose registers.

• The Accumalator : This is used to temporary hold values while operations is still being performed.
• The Instruction Counter: This is used to hold the memory location of current instruction.
• The Instruction Register: This is used to hold the current instruction being performed. It consist of two parts.
  • operation: The operation being performed. This is one of the 12 instructions of the simpletron.
  • operand: The memory address the operation is working with.

Instruction set

The simpletron contains 12 instructions divided into four categories.

Input and Output Instructions

These instructions handle the basic input and output of the simpletron

Name	Code	Description
READ	10	Read a word from the terminal into a specific location in memory
Write	11	Write a word from a specific location in memory to the terminal

Accumulator Instructions

These instructions are used to work with the accumulator.

Name	Code	Description
LOAD	20	Load a word from a specific location in memory into the accumulator
STORE	21	Store a word from the accumulator into a specific location in memory

Arithmetic Instructions

These instructions handle arithmetic operations

Name	Code	Description
ADD	30	Add a word from a specific location in memory to the word in the accumalator and then leaves the result in the accumulator
SUBTRACT	31	Substract a word from a specific location in memory to the word in the accumalator and then leaves the result in the accumulator
DIVIDE	32	Divide a word from a specific location in memory into the word in the accumalator and then leaves the result in the accumulator
MULTIPLY	33	Multiply a word from a specific location in memory to the word in the accumalator and then leaves it in the accumulator

Control FLow Instructions

These instructions are used to alter the flow of the program

Name	Code	Description
BRANCH	40	Branch to a specific location in memory
BRANCHNEG	41	Branch to a specific location in memory if the accumulator is negative
BRANCHZERO	42	Branch to a specific location in memory if the accumulator is zero
HALT	43	Halt the program