Retro Challenge – Getting inside the matrix

So, today I finally did some hands-on retro wires and programming stuff instead of sitting at a PC doing CAD stuff.

I thought I knew how the LED matrix modules would work, in theory, but before I commit anything to copper and fibreglass, I’d like to test things out a bit.  So I dug out my breadboard Z80 and fired it up to check it still worked (it did), and refreshed my memory on how the BASIC “OUT” command works with the ‘374 latches.  Finding a bit of space on a breadboard, I plugged one of the modules in and wired it up in place of the bar graph and 7-seg displays I’d previously used as channel 0 and 1

I wanted to get a single dot on the display, so that meant turning the various pins high or low.  One channel needed a single pin high with the other channel all high except for one pin.  Or the other way around.  Or just one pin on both channels.  Or, maybe all high except for one on both channels.  I could have gone through and calculated exactly which combination to use, but it was quicker to try everything.  But I got very weird results


Something wasn’t right.  I was scratching my head for a while until it dawned on me that the pin-out diagram on the datasheet was ambiguous (to me at least) and I’d taken it the wrong way.  So, after rewiring pins 1-8 to 8-1 and 9-16 to 16-9 I tried again.  BINGO!

So, using the best of my artistic and BASIC programming skills, I set about creating a little 8×8 icon


Much better!


If you squint your eyes, and turn your head 90 degrees… no, 90 degrees the other way! you can kind of see a grinning smilie face!

So, using MS BASIC I’ve proved the LED matrix displays work with the Z80 hardware.  I’m happy that a few of these together will give a big enough display to have something more meaningful than a grimace on it.  I think I’ve lost the window of opportunity for getting PCBs made up for these though, so it’ll have to be a breadboard or veroboard build to complete the challenge.

It now comes down to the PCB fab house to make and deliver the Z80 circuit boards, and my ability to learn programming in Z80 assembly language.  The latter is my biggest worry.