Inspiration for this mode I found on Daryl's Computer Hobby Page. Daryl made Composite Video Text/Graphics Display based on ATMEGA8 and drive by VIA6522. This article will show how to build, assembly and connect VIA 6522 IC to Atari and use 2 additional 8-bit parallel ports and serial interface. This is my own project build from scratch but it's nothing modern - this IC was used in C64 to communicate with disk drive. It will be used as additional PIA for manage other equipment.
Well, on the market you may find a few sellers which have VIA6522, but...
- this IC is discontinued, don't wait so much time, buy it!
- it's still very useful and may be good alternative for PIA 6520(6521).
- topology and registers covering PIA 6520, so you may use it as equivalent for it. (some pins should be swapped)
- very cheap IC (~2$/piece).
Prototyping and Manufacturing
As last time (SRAM 512k extension module) I made the schematic and PCB using KiCAD (actually I'm so surprised how good is this software!). Below you my find schematic and PCB layout:
Prototyping on the breadboard: PCB layout: ...
PCB without elements: Assembled PCB: And finally, mounted into Atari: Test procedure
Actually it's very easy and dummy test - just only for checking that 6522 working properly:
Enter the short program in BASIC interpreter and type RUN:
Now you may observe state of both ports on 6522 device. The simplest test is when you will connect any PA/PB pin to GND...
Code: Select all
10 ? PEEK(54528);: ? " ";: ? PEEK(54529) 20 GOTO 10 RUN
Well many ideas to do. Now you have independent ports. For example you may steering 64 LED matrix... using SERIAL port and many many more... I'll try to build additional display adapter as mentioned on the beginning of the article.