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Old 03-27-2008, 05:15 AM
sje sje is offline
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Join Date: Nov 2006
Posts: 62
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I have a real Apple IIe I bought via a Usenet ad many years ago. Alas, it no longer boots and only displays gibberish on the screen. I never used it much, so it looks like I never get around to diagnosing and repairing it.

My own little project is breadboarding a W65C02S system with a fully functional front panel. Unlike Grant's projects, it isn't a replica of anything; rather, it's just plain retrocomputing. The W65C02S is a fixed up version of the original 6502; it's implemented in CMOS and can be run or stepped at any speed. Well, any speed below 14 MHz. My idea for the front panel is to have it be run by an Atmel AVR (only $14) and include full bus display and 6502 register access. But unlike any front panel machine I've ever seen, it will have a serial link (supplied by the AVR) that will provide a complete remote access facility. Each switch on the panel will be implemented with a momentary contact and so can be operated in "soft mode". The panel could even have an IR photodiode so I can use a handheld IR remote control.

A program load can originate with a typical computer connected to a USB/RS-232 converter that connects to the front panel AVR. At 19,200 bps the typical computer can tell the AVR to load 56 KB of RAM in about 30 seconds with a nice light show as a side benefit.

My idea is to use 64 KB of static RAM but map the upper 8 KB of the memory space to a boot PROM and various I/O chips. (The 6502 uses memory mapped I/O exclusively.) I'm also considering adding a second AVR accessible by the 6502 for I/O, timers, etc. This AVR could also be used to implement a TCP/IP stack and a physical Ethernet connection. Another idea is to have the second AVR run a compact flash card emulation of a disk subsystem.

What else? A non volatile real time clock and calendar chip. Maybe a speaker, and maybe several piezoelectric buzzers of different frequencies. Or an X10 control node. A cassette tape interface, maybe one that controls my little solid state voice recorder and its sixty hours of indexed audio storage. A modem with caller ID support so the machine can hang up on annoying solicitors. Possibly an MP3 player, although I think this would be a bit taxing of the 6502 capabilities. And then there's the obvious possibility of a retro video and keyboard interface. A D/A converter that runs an analog front panel meter that indicates processor utilization. A papertape reader, if only I could find an inexpensive papertape punch.

It may be that the initial breadboard realization won't run at a full 14 MHz, so I'm considering a wirewrap version the second time around. (The great mystery: why do wirewrap chip sockets cost more than some of the chips themselves?) I could eventually produce a two board design (panel on one PCB, 6502 system on the other) although I might need a little help on this. A case and power supply shouldn't cost too much if appropriate off the shelf products can be had cheaply.
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