an example of my work from 1980
And believe it or not, I can still power it up and it still works. More or less...
One reason I hang onto this board is the one lone chip from Rockwell International (you can see the logo on the lower 6522 chip), the conglomerate that made the Space Shuttle. Rockwell also had a chip division, and I picked up a kit of their industrial grade semiconductors back in the day. This board was initially meant for harsh industrial environments, not shirt-sleeve office areas.
Here were the specifications in a nutshell.
- 4MHz 65C02 (before I put the board away in the garage, I upgraded the processor to a 65C802 and began to dabble with the extended 16-bit instructions).
- Full 64K decoded address broken up between 48K SRAM, 16K EPROM, with 1K I/O. The SRAM addressing lost 1K to the I/O block.
- Zero wait state/non refresh memory allowing for full 4MHz performance.
- Western Digital WD 1770 IBM format compatible single-chip floppy disk controller (long since removed for another project). The Rockwell 6522 provided additional I/O controls on the floppy connector (see far left edge).
- Phillips Electronics SCC 2692 Dual Universal Asynchronous Receiver/Transmitter (DUART). These chips came with separate input and output ports as well as full blown UART control pins, baud rates up to 38.4K, quad buffer registers, and timers. I had two on the board at one time, one was taken off for another project.
I'd gone to the trouble to write 6502 assembly routines to read, write, and manage the floppies using the MSDOS file system. That meant I could use an IBM PC with 3.5" floppies installed (720K only) as an intermediary to set up the floppies, writing files I could read via my SBC. I hated how Woz had created the floppy controller and totally incompatible floppy format for the Apple ][, and I was no fan of the Commodore 1541 floppy drive either. When it came time to add disks to my SBC, it was IBM format compatibility with MSDOS support all the way.
In this age of multi-gigabyte, multi-gigahertz cell phones, something like this limited and slow look ludicrous. But back in 1983 when it was finished it was a decent tool for driving other computers for testing. And when I finally added my modified C-64 Basic to the toolkit, it because even more flexible. It was the computer I wanted, something that was powerful and flexible and anywhere from four to eight times faster than the C-64 and the Apple ][ at that time. But I didn't push to productize it because I already saw the writing on the wall with the 16- and 32-bit processors that were hitting the market. For example, in 1985 I picked up a Compaq Computer 80386 computer as a loaner for evaluation. Just two years after I finished my SBC, and one year after adding a hacked Basic to my SBC. And keep in mind that the IBM PC was introduced back in 1981, and it was based on a 4.7MHz 8088, a 16-bit internal processor with an 8-bit buss.
It's fun to pull out, and I could probably re-create this board with up-to-date parts and probably my old firmware source code reassembled for the new hardware. But that would detract my attention away from the 6502's spiritual descendant, the ARM processor and all the products built with it, like the majority of today's smartphones.
And I'll be writing about that in fairly short order.