Expansion bus

Using, learning, programming and modding the Gigatron and anything related.
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Joined: 13 May 2018, 08:26

Expansion bus

Post by marcelk » 01 Nov 2018, 16:22

As originally designed there is no direct expansion bus on the Gigatron, and that creates a bit of a HW bottleneck especially when wanting to do more serious I/O. One of the great things of the Altair 8800 was of course that it set the S-100 standard. The RC2014 has a similar concept.

Pondering about this from time to time, I dawned upon me that all ingredients seem to be in place to add one without modifying the board: the RAM socket.

The idea is that it has address lines, data lines, a R/W line, Vcc and GND already. We could put a pin on the breakout point for A15. The RAM gets no clock signal, but there is a test point nearby for CLK1 (next to U16, the OR gates) and we can do the same there.

So the question is: would that work? Make a daughterboard that plugs into the RAM socket, A15 and CLK1. It would have its own socket to reseat the RAM, but also a header connection to break out all of these bus signals. Probably some protection and/or buffers, maybe a decoder for high address lines.

Any thoughts?

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Joined: 02 Nov 2018, 08:45

Re: Expansion bus

Post by nutson » 07 Nov 2018, 10:02

I would love to see a board with additional I/O capabilities. I was already planning to assemble a gigatron board with a wire wrap socket for the RAM to be able to connect a hand wired expansion board (with a good old 8255 chip?) on the back of the Gigatron.

My application would be a project with many WS2812B LED's (and a Parallax Propeller driving the 800 KHz LED refresh chain) where the Gigatron in its beautyfull case would shine as the Master controller. As a minimum the Gigatron would need to be able to read a keyboard/joystick (speed/intensity/pattern up/down) and output a (parallel) status word to the Propeller).

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