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68 Katy Schematics and Parts List

A number of people asked for a parts list and schematic for 68 Katy, so they could build their own version. Here it is! Please let me know if you find any errors.

 
Parts List

  • Motorola 68008 CPU, 8 MHz, 48-pin DIP package
  • AM29F040B 4 megabit Flash ROM
  • BS62LV4006PIP55 4 megabit SRAM
  • Sparkfun FT245RL USB to FIFO breakout board
  • 2 MHz metal can oscillator
  • NE555P timer, 8-pin DIP package
  • 74LS139 decoder
  • 74LS377 8-bit register
  • 74LS244 8-bit tri-state driver
  • 74LS00 quad NAND
  • 74LS08 quad AND
  • 74LS32 quad OR
  • Lattice GAL22V10D logic array
  • bypass capacitors, resistors, LEDs, buttons, etc.

The GAL was used to replace some of the glue logic that would otherwise have required more NAND’s, OR’s, flip-flops, etc. If you’re building your own version of 68 Katy, you don’t necessarily need the GAL. Just replace it with the equivalent 7400-series basic logic gates.

 
Memory Map

00000 - 77FFF : ROM
78000 - 79FFF : serial in
7A000 - 7BFFF : serial out
7C000 - 7DFFF : serial status
7E000 - 7FFFF : LED register
80000 - FFFFF : RAM

 
CPU

68katy-schematic-cpu

 
RAM and ROM

68katy-schematic-memory

 
Control Logic

68katy-schematic-control

 
555 Timer for Scheduler

68katy-schematic-555

 
USB Serial FIFO

68katy-schematic-ft245serial

 
LED Display

68katy-schematic-LEDs

Read 2 comments and join the conversation 

2 Comments so far

  1. Charles November 28th, 2014 6:24 pm

    pcb? or then it wouldn’t be true to big mess of wires? lol

  2. Sherry Haibara November 30th, 2014 11:03 am

    I think one could design its own PCB if he really wants it, but it would kind of defeat the whole simplicity of the project! To me the most beautiful thing of this design is that it’s very compact, extremely easy to build and to understand even for non technical people: I mean, it’s only a handful of off-the-shelves components, no soldering skills required and there are only four breadboards to handle!
    Personally I’m very thankful to Steve for having pursued this project, it’s really true to the homebrew tradition and it makes possible for people grown up after the 70s to live some of the emotions that one could have experienced back then, when the computer industry was still in its infancy. I’m really looking forward to building one during this holiday season!

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