This is my 8-bit SAP that i build watching ben eather youtube playlist.

While studying the 8085 microprocessor, I was looking for resources to deepen my understanding of its internal workings. I came across the r/emudev subreddit, where I saw people building interesting projects in Logisim. This led me to discover Ben Eater's 8-bit SAP-1 YouTube playlist. After completing my studies on the 8085, I went through the entire playlist and implemented the SAP-1 in Logisim.

Video Demonstrationf of it doing Division 45/6 using repeated Subtraction

Another demo of it doing a multiplication 5x8 program using repeated addition

You can check out a recorded demonstration of the Division program on my Twitter post here.

This project simulates a simple 8-bit computer with the following key components and specifications:

• Registers:

  • Accumulator: An 8-bit register for arithmetic and logic operations.
  • B Register: Another 8-bit register used in conjunction with the Accumulator.
  • Temporary Register: An 8-bit register used during instruction execution.

• Program Counter (PC): A 4-bit parallel load register that keeps track of the next instruction to execute.

• Memory Address Register (MAR): A 4-bit register that holds the address of the memory location to be accessed.

• RAM: 16 bytes of memory used for storing both data and instructions.

• Instruction Register (IR): An 8-bit register that holds the current instruction being executed.

• Arithmetic Logic Unit (ALU):

  • Performs 8-bit addition and subtraction.
  • Affects the Carry and Zero flags based on the operation results.

• Control Logic (Instruction Decoder): Implemented using a 1K x 20 ROM that decodes instructions and generates control signals.

The instruction set includes the following commands:

• LDA: Load the Accumulator with the contents of a memory location.
• ADD: Add the contents of a memory location to the Accumulator.
• JMP: Jump to a specific memory location.
• JC: Jump to a specific memory location if the Carry flag is set.
• STA: Store the contents of the Accumulator in a memory location.
• ADI: Add an immediate value to the Accumulator.
• SUB: Subtract the contents of a memory location from the Accumulator.
• OUT: Output the contents of the Accumulator.
• JZ: Jump to a specific memory location if the Zero flag is set.
• SUI: Subtract an immediate value from the Accumulator.
• HLT: Halt the execution of the program.

With the above instructions, this computer can:

• Move data in and out of RAM.
• Perform arithmetic operations on data stored in registers.
• Execute unconditional and conditional jumps.

These functionalities make the computer Turing Complete. There is still space left for 4 more instructions to be added.

Below are the resources that I've used: I started by stuyding about microprocessor 8085 and microcontroller 8051 while studying about them i came across ben eater youtube channler and emudev subreddit, I was amazed by looking at the cool projects people were building so thats how i decided of building a simple implementation.

In order to program it you need to set toggle_address_mode & prog_bus_toggle pin to 1 and then you can feed the memory address through the prog_addr and can input the instructions through prog_data.

• EEEGUIDE Blogs: Blogs for studying the 8085 microprocessor and 8051 microcontroller.
• Digital Fundamentals (11th Edition) by Thomas L. Floyd: Book for digital fundamentals.
• Ben Eater's YouTube Playlist on 8-Bit SAP: YouTube playlist for building an 8-bit CPU.
• Emudev Subreddit: Community for support and discussions related to emulation and low-level programming.

===> A MULTIPLICATION PROGRAM USING REPETITIVE ADDITION

===> A DIVISION PROGRAM USING REPETITIVE SUBTRACTION

===> A FIBONACCI SEQUENCE GENERATOR PROGRAM