SheMachine - a small expandable 65c816 computer

[Shaos]

https://hackaday.io/project/2993-shemachine

DESCRIPTION

What could be more fun than than to build a nice 65c816 computer. The core system has 1M SRAM, 256K EEPROM, Serial, VGA, RTC and SD card Interface. Open Architecture allows memory expansion, Commodore SID board or other "cool" feature creep.

DETAILS

A couple of years ago I caught a bug on the idea of building my own computer. Now I have seen this done but for some odd reason fate has never tempted me to build one myself and learn to program that machine in its own language. The core of the machine is the 8 or 16 bit 65c816 made by Western Design Center, Bill Mench who runs the outfit is also one of the central figures in the design of the 6502. To make a long story short the 16 bit cpu is compatible with the venerable 6502 code. The 6502 is arguably the most popular CPU in history Its still being today in many applications. The 65816 on the other hand did not take off like its little brother. Offhand I can only think of a few machines that put it to work like the APPLE IIGS, Then there were accelerator cards that put the main computers 6502 to sleep and then the 816 took over. Overall the 816 was a little late to the market and never gained its much needed popularity. The biggest death Knell to 65xx based processors was the attitude that a computer was like an appliance, not upgradeable. The XT was a leap in forward thinking, in the fact that the hardware you bought could be moved to the next machine. People became disenchanted with the idea of buying a whole new computer and accessories every couple of years and opted to go with PC compatible hardware, Even Apple had held that opinion way late in the computer industry. As their mac line was not upgradable. So I have decided to make this one more than just a simple board with some blinking lights. This puppy is going to be expandable, and a hack at home funbox.

The basic system contains 1MB of SRAM, Its moderately cheap fast and easy to interface to. Dram requires ram refresh lines and timing and I really dont have time to fiddle with that right now. Perhaps later a board could be made to interface in the expanded area. Since the IO is all on an in system programmable CPLD the memory map can be moved around to change the memory map.