6502

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Code for 6502 BIOS, ROM Programmer, Arduino Interface and Java Terminal

// repository documentation

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## 6502
This project contains the sources created while bread-boarding a 65C02 CPU from an old Apple IIc.

### Hardware
The breadboard contains the following items:

* [65C02](https://en.wikipedia.org/wiki/WDC_65C02)
* [Teensy 2.0](https://www.pjrc.com/store/teensy.html)
* 32kx8 SRAM
* 8kx8 ROM
* 16x2 LCD Display
* 74HC139, 74HC04 and 74LS03

Optional components are required when building your own programmer :)

![alt text](https://github.com/djBo/6502/raw/master/65C02_Breadboard.jpg "65C02 on a breadboard")

![alt text](https://github.com/djBo/6502/raw/master/Programmer_Breadboard.jpg "Programmer on a breadboard")

### Memory Map
The bottom half of RAM is occupied by a single 32kx8 SRAM ic. The top half is decoded using a 74139 2-to-4 decoder. The Teensy 2.0 micro-controller sits at `0x8000`, a 16x2 LCD sits at `0xA000`, and the 8kx8 *ROM* occupies `0xE000` to the end.
The address decoding came from [here](http://www.hytherion.com/beattidp/comput/x65tools/diy6502/diy6502.htm), written by Douglas Beattie Jr. His schematic (as shown below) is the basis of my implementation.

![alt text](http://www.hytherion.com/beattidp/comput/x65tools/diy6502/diy6502.gif "DIY 6502")

### Operation
The Teensy provides `CLK`, `RDY`, `RES` and `IRQ` signals. It also acts as a device on the bus and provides a remote terminal.

### LCD
The LCD screen is attached using this [howto](http://6502.org/mini-projects/optrexlcd/lcd.htm) written by Chris Ward. You can see I included pretty much all his example code into the BIOS.

![alt text](http://6502.org/mini-projects/optrexlcd/lcd6502.gif "LCD Interface")

### Code
* bios.asm
  * The main assembly file to be burned on the 8kb ROM module
  * Assembles using [dev65](http://www.obelisk.me.uk/dev65/) (see the Makefile)
* IO65.ino
  * The main program to be used on the Teensy 2.0
* Programmer.ino
  * The main program to be used on a Teensy 3.1
* Programmer.java
  * To be used to `LOAD` data from the PC to the Teensy 3.1
  * `SAVE` not implemented
* Hex2bin,java
  * Simple program to convert HEX data into binary

### Programmer
The programmer for the ROM is a complete side-story on it's own. It consists of a Teensy 3.1, two MCP23017 16-bit port-extenders and a level converter. The connections are very simple and explained in the source.

6502

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