README.md

Intel 4004 emulator with very reduced functionality

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Introduction

In September 2023, I decided to sign up for Future Code in order to gain knowledge of the Python language. Alas, after a very long period of time (until October), after filling out all the paperwork and so on, we were told that because of two, pardon the expression, morons who didn’t get something and somewhere in time to fill out and pass, had to cancel this program in my technical school. I was not really upset, on the contrary, it even gave me a good impetus. to learn this programming language on my own at home, as I did with all previous languages :) My last projects were video games, so this time I decided to write something more serious, namely a CPU emulator, specifically Intel 4004 with very reduced functionality. Bottom line: I got it all (not at once), but it worked and I want to share this creation with you, dear comrades!

As of April 2024, the emulator has been rewritten from scratch and is currently under active development.

About the emulator

The emulator has 256 bytes of memory into which program results are stored.

There is the Accumulator (acc), a processor register in which the results of arithmetic and logical instructions are stored, program counter (pc), a processor register that indicates which instruction to execute next, and a carry flag (carry) that indicates the occurrence of a one as a result of an arithmetic operation.

An opcode, a piece of machine language called an instruction that defines the operation that to be performed. Here is a table of opcodes and their corresponding operation:

Opcode Operation
0x0 No Operation
0x1 Jump conditional
0x2 Fetched immediate from ROM
0x4 Jump unconditional
0x5 Jump to Subroutine
0x6 Increment index register
0x7 Increment index register skip if zero
0x8 Add index register to accumulator with carry
0x9 Subtract index register to accumulator with borrow
0xA Load index register to Accumulator
0xB Exchange index register and accumulator
0xC Branch back and load data to the accumulator
0xD Load Data to Accumulator
0xF0 Clear both
0xF1 Clear carry
0xF2 Increment accumulator
0xF3 Complement carry
0xF4 Complement Accumulator
0xF5 Rotate left
0xF6 Rotate right
0xF7 Transmit carry and clear
0xF8 decrement accumulator
0xF9 Transfer carry subtract
0xFA Set carry
0xFB Decimal adjust accumulator

How is the program set up?

You should make the program directly in the code, specifically in program.py. Here is an example program where the number 5 is subtracted from the number 12 and then the number 2 is added:

cpu.memory[0x10] = 12
cpu.memory[0x11] = 5
cpu.memory[0x12] = 2

cpu.LD(0x10)
cpu.SUB(0x11)
cpu.ADD(0x12)
cpu.NOP()

Additional material

Intel 4004 datasheet

About license

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.

Описание

Intel 4004 emulator with very reduced functionality in Python.

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