Intitial commit

Author: Bruno Conde

.gitignore

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+.DS_Store

README.md

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+I started following the [Ben Eater's awesome tutorials](https://eater.net/6502) to create my own retro computer using chips from the golden age of PCs. The 6502 and the z80 CPUs started the personal computer revolution back in the 70s and 80s.
+
+Therefore, the plan is to build a very simple computer using one of these CPUs, a ROM, RAM, IO, Serial, and other logic chips.
+
+I needed a way to flash the EEPROM.
+
+<p float="left">
+  <img src="/assets/IMG_0759.jpg" alt="Arduino EEPROM programmer photo 1" width="200px" />
+  <img src="/assets/IMG_0760.jpg" alt="Arduino EEPROM programmer photo 2" width="200px" />
+</p>
+
+# Description
+
+The goal of this project is to provide a way to flash a ROM file in an EEPROM chip using an Arduino Mega. The EEPROM chip that I'm using is the ![AT28C25615U from ATMEL](/assets/eeprom_AT28C25615U.pdf).
+
+I decided to use an Arduino shield with a ROM socket to flash a ROM file from my computer to the EEPROM.
+
+The first step was to solder a bunch of wires for the address and data bus. There are also 3 control lines for the **Write Enable**, **Output Enable**, and **Chip Enable** pins specifically, that I needed to redirect to the Arduino as well. There are a total of 16 pins I need to control and the Arduino Mega is great for this job as it has enough digital pins. Using an Arduino Uno (or mini) is also possible, provided that we [use shift registers for the address lines](https://www.youtube.com/watch?v=K88pgWhEb1M).
+
+# How it works
+
+I created a small program (which you can find in this repository) for the Arduino to read and write the EEPROM.
+
+There is also a Python program to flash a ROM file using the Arduino serial port. I reckon I was too lazy to implement a protocol like xmodem to allow a program like "screen" to upload files directly to the Arduino without the need for an additional script.
+
+The Arduino program has the following options:
+    1 - Read ROM
+    2 - Write ROM
+    3 - Read byte at address
+    4 - Write byte to address
+    5 - Erase ROM - 6502 NOP
+    6 - Erase ROM
+
+This menu is displayed when the Arduino is connected using a serial interface (e.g. Arduino monitor, or using a tool like screen or putty). 
+
+Option 2 provides the ROM flashing capability. Of course, updating a ROM file using the monitor (or any other serial connection) is not practical as you need to type or paste the ROM into the monitor input.
+
+This was the reason that I created the python script. This script is just an interface between the Arduino and a computer. Right now, the script only flashes the ROM file. 
+
+All remaining options can be accessed using a serial interface.
+
+
+# How to use
+
+## Flashing a ROM file into the EEPROM
+
+Required libs:
+```
+> pip install pyserial-asyncio
+```
+
+Running the script:
+```
+> python flash_eeprom.py <UART> <ROM_FILE>
+```
+
+Example (macOS):
+```
+> python flash_eeprom.py /dev/cu.usbmodem1413401 rom.bin
+```
+
+## Serial Interface
+
+**Baud rate: 115200**
+
+If you need to use any of the other options (Reading, Writing At, Reading At, and Erasing), please use a serial tool like screen or putty to connect to the Arduino.
+
+Example (using screen in macOS):
+
+```
+screen -S eeprom_prog /dev/cu.usbmodem1413401 115200
+```