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TPC65 - History: The PCB Age

Version 1.0

Even though the protoboard computer works, and I successfully worked with it for months, it has some significant drawbacks:

  • Difficult to modify
    • Making any changes to the system requires maneuvering through a trunk of wires with an iron.
  • Fragile
    • Multiple wires are often joined to a single pad. This requires the solder joint to be reheated/reflowed multiple times. A wire that pops loose would be difficult to reattach.
  • Not worth reproducing
    • It took about three days of soldering to get the computer connected. Repeating that task is not something I was looking forward to.
The obvious solution is to make a PCB version of the board. It always seemed kind of silly to me to make a PCB version of a one-off project. But, it's either that or doing it all by hand again. So, after following along with the excellent KiCAD tutorials by Shawn Hymel, I set out to put the computer onto copper. 

A tricky thing about computers of this era is managing the bus lines between devices. The most common approach I've seen is the X-Y approach, where you have traces run top-to-bottom on one side, and left-to-right on the other. This allows the traces to be a lot straighter with the trade-off of needing a lot more vias to connect the traces between layers.

Because I wasn't sure if this was even going to work (and because I'm cheap) I set out with the goal of making the PCB as cheap as possible to fabricate. This meant keeping the board to 100x100mm and two layers.

The first attempt was a direct copy of the hand-soldered computer, including all the mistakes made during construction:


The two boards shown above are functionally identical. Apart from one trace mistake, I only needed to move the components from board-to-board and it worked perfectly fine. 


Version 2.0

The next step was to finally commit the improvements I wanted to make on the original computer. These improvements included:
  • Fixing the mistakes made during construction
    • Specifically aligning the bus lines with the Arduino Nano's ports for faster bitwise operations.
  • Adding a second VIA
  • Adding a dedicated SD card port
    • Utilizes port A of the first VIA

 And this, version 2 was born:




Version 3.0

As of writing, I'm currently working on the next version of the computer which will replace the 65C02 with a 65C816, the 16-bit successor to the 6502.

In the next post, I'll detail more about the theory of operation of these computers and the supporting software.
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  1. liamApril 14, 2023 at 2:36 AM

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    ReplyDelete

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