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Retrochallenge started! Step 1 schematics and wiring done.

A project log for RC2016/99: TI-99/4A clone using TMS99105 CPU

Retrochallenge 2016/10 entry and winner: try to build a TI-99/4A clone using a TMS99105 CPU and an FPGA. In a month...

erik-piehlErik Piehl 10/01/2016 at 20:360 Comments

Oct 1st is almost now over, so Retrochallenge 2016/10 has officially started and so I did start working on the project.

The first step was choosing which FPGA board to use, designing the step 1 of the schema to interconnect to that board and wire up the circuit in the diagram. I wanted to use my new Saanlima Pepino board, so I went with that. I ordered and received this board about a month ago. I also ordered their buffer board. Alas, it turned out that there we no schematics for the buffer board, so working on the schematics was harder than I expected since I needed to decipher how the buffer board connects to the FPGA chip. Below is the schematics I came up with. This is not enough for this whole project but is the starting point. For now the minimum amount of signals is wired up.

I also wired up the board (built on a protoboard in accordance to the schematics). Next I need to double check everything and find the courage to power on all of this, hoping nothing blows up. I haven't done any FPGA design work yet, so all I could check for now is that basic signals work but the system will not do anything meaningful before the FPGA is ready. Below is a picture of the current wiring. Nice mess of wires.

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