Monthly Archives: August 2019

Rebuild Update

All of the 3.3V parts for the new COLE-2 prototype have arrived, and I’ve begun the slow process of rewiring everything. I am hopeful that this rebuild will eliminate my stability problems from the previous version, and also possibly get up to a target speed of 6.25 MHz.

In addition to increased stability, this rebuild is allowing me to reconcile what I have built vs what I have drawn on the schematics. Up to this point the design in the schematics has been lagging the actual hardware, because I was making so many design changes. This time around I’m doing things right: schematic first, then build.

Before I started any wiring I experimented with various breadboard layouts and chip positioning. In the end I opted for six breadboards, oriented vertically and arranged left to right. This, plus some careful chip placement will make the wiring of the data and address lines much easier. And, with six full boards, I can now fit all of the planned features into this build and still have plenty of room left.

Here’s what the build looks like at the moment, with all of the power rails connected and about half of the data bus wiring done:

The six boards, from left to right, are:

  1. The TinyFPA and VGA connection. I’ll be adding some 74LVC245 buffers here for the address & data bus connections soon.
  2. The XC9572XL CPLD, which is replacing both of the GALs from the previous build.
  3. The 65816 CPU (bottom), plus the 74LVC245 data bus buffer (top) and the 74LVC573 bank address latch (middle).
  4. The first 512 KB static RAM (top) and VIA #1 (bottom)
  5. The second 512 KB static RAM (top), VIA #2 (middle), and the ATmega328p (bottom; this may move)
  6. The 512 KB flash ROM (top) and the 28L92 dual UART (bottom)

I don’t expect the rebuild to be done for at least a couple of weeks. I have learned that if I speed up the build I get impatient and end up doing sloppier work. So, I’m going to just do a little bit of wiring every day while I work on more interesting things, like the new VGA implementation. I think the end result will be much better off that way.