RC2014 - Part 1

A quick introduction if you are reading this and have never heard of the RC2014…. it is a kit computer created by Spencer Owen and available from https://rc2014.co.uk.  Notes on the history of the RC2014 are at https://rc2014.co.uk/history/

If you have read other parts of this blog you will likely notice that most retro machines mentioned are based on the Z80.  You can blame this on my first introduction to a microcomputer was with a TRS-80 model 1. 

I first discovered the RC2014 when Hack-a-Day published a review in 2016.  At the time of writing the review is still available at https://hackaday.com/2016/09/08/review-the-rc2014-z80-computer/

I thought it was interesting but having already built Grant Searle’s 7 chip design, both point to point wired and on PCB, Sergey Malinov’s  Zeta V2, rehabilitated a number of other Z80 machines and was in the process of building S100 boards from S100 Computers, I didn’t see it as a compelling design, for me anyway, as someone happy to build things from components and prototype board. 

What I didn’t realize, but it dawned on me in early 2018 was that RC2014 is a great Z80 hardware hacking platform.  The Searle and Malinov single board computers are nice compact designs but not so easily expandable.  S100 is certainly expandable but the board size and interfacing requirements do push up the price to experiment.  Most RC2014 boards are less then 100mmx100mm so you can get 10 boards from many of the “cheap PCB” manufacturers for less than the price of a single S100 board.  It helps to have a few friends to share the surplus.

The first step in my RC2014 adventure was to build a backplane.  Spencer has the official RC2014 boards available from his store on Tindie and there are also several alternative (but compatible) designs but I had a couple of reasons to build my own:

  • Learn Kicad (seeing as my free Eagle license won’t let me build a board that size).
  • Fully understand the design.
  • Use an extended bus similar to the one described here because I want to try making a 68000 processor board.
  • Be able to share the surplus boards with some friends here in New Zealand.  The more local builders the better to keep motivation.

The result was a 7 slot backplane with 78 pin extended bus sockets. The board was produced by Dirty PCBs (https://www.dirtypcbs.com), a supplier I have used often and with whose boards I have always been happy with.  It also helped that they offer an option of 2mm board thickness which I used for the backplane…. a good choice to reduce flexing.


Other features of the backplane include:

  • A 5v switching regulator in place of the commonly used 7805.  These are available on Aliexpress in TO-220 form factor and are a good alternative for a backplane with a higher current draw from many installed boards.
  • MC34064 reset controller.  This TO-92 sized package will hold the /RESET line low until the backplane power has stabilized.  A jumper is provided to connect (or not) the MC34064 to the bus /RESET line so the backplane can be used for boards that have their own reset circuit.
  • Momentary Reset switch.
  • On/off Power switch.

What would (will) I do differently for the next batch of boards?

  • Use an 80 pin (2 x 40) rather than 78 pin (2 x 39).  It saves cutting the sockets or removing pins.
  • Larger bus track isolation pads.  The 0201 resistor pads that I put on selected bus tracks so section of the board could be isolated looked more than big enough to solder on Kicad… they certainly are not on the final board.


 
 

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Contact Andrew Quinn

jaquinn@ihug.co.nz http://twitter.com/jaquinn