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Retro Challenge – The inbetween days

So, after a flurry of activity, blog posts and updates at the start of the month, things have got a bit quiet.

That’s not to say I haven’t been doing anything.  I have.  Lots.  But nothing really specific or bloggable.

Until the batch of PCBs arrive, I am kind of in limbo land.  However, I’ve been looking in to the LED matrix boards a bit more, and working out how I’m going to connect them up (short answer – use breadboards to complete the challenge, but get PCBs made up for long term mounting.).

As the breadboard Z80 runs Microsoft Basic, I have been using that to test out a few bits in terms of orientation of the matrices and the best way to drive them.

0,1 - 1,254 0,1 - 1,1270,128 - 1,127 0,128 - 1,254

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Retro Challenge – Font Selection

So, if I’m going to write my name on a bunch of 8×8 LED matrix displays, I have a couple of options; Write my name on grid paper, colour in the squares, convert it to binary and transpose it to hexadecimal.  Or… I could use a font that’s already out there.  Like the one that Sinclair used in the ZX Spectrum.

I’ve already got a copy of the Spectrum ROM, and, handily enough, all the characters are right at the very last part of the ROM address space (from 0x3D00 to 03FF), in consecutive blocks of 8 bytes.

I can see this coming in handy later! (more…)

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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

IMG_20140707_205635 (more…)

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Retro Challenge – Day Off

So, having had a few fairly intensive days working on PCB design for my RC2014 computer, today was pretty much a day off.  Apart from daily household chores, all I got done today was this;

Screenshot from 2014-07-06 22:41:19

Now, to the untrained eye, that may look like a schematic layout for 4 8×8 LED matrix displayed connected to a Z80 bus via some 74LS374s.

But it’s not. (more…)

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Retro Challenge 2014 – Day 5 – First PCBs Ordered

Hokey cokey, that’s the first 4 printed circuit boards for the RC2014 (Oh, did  tell you I’ve named my homebrew Z80 computer “RC2014”? Pretty catchy name, eh?) ordered with OSHPark.  If they arrive as quick as other boards I’ve had from there before, then I should have 11 days to get everything put together and working!

All 4 boards look fairly similar, being a CPU board, RAM and 2 variation on ROM, but here’s the 32k RAM board;

Screenshot from 2014-07-05 16:02:42 (more…)

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Retro Challenge – Day Something

Ok, it the 4th day of the Retro Challenge, and this is just a quick blog update about what I did yesterday, which was my 2nd day of doing Retro Challenge stuff.  So, yeah, it’s Day Something.

Due to life getting in the way, I didn’t get an early start last night, but I did have time to do 3 schematic and 2 PCB layouts for my Z80 that I’m building.

The first board will be for a 2764 EPROM that’s programmed with Microsoft BASIC.  Technically this is not part of RC for me, but I know MS BASIC works on my breadboard Z80 so it’ll be an easy and convenient way to test out the hardware.

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