-

Retro Challenge – Z80 Assembler Breakthrough

Sorry I’ve not made any updates for a couple of days, but there’s not been much of significance to report of late.  Until today, that is.  Although, as far as the PCBs I’m waiting for are concerned, the only news to report there is that there is no news to report.  I will report tomorrow if there is news to report on this or not.

I have, however, been plodding away at teaching myself Z80 assembler language.  And with some progress too!  I’ve managed to pass the first major milestone with the code I’m writing to display text on the LED matrix displays!  It basically, looks at some text stored in a memory location, then looks up each character in turn on the ASCII character map that I lifted from a ZX Spectrum ROM, and puts each line in every 5th byte in a different location.  This new location is essentially a 40 byte screen map for the matrix

Screenshot from 2014-07-23 21:00:25

(more…)

-

Retro Challenge – The Matrix Reloaded

The 5 matrix board has now been finished. And no one could be more relieved than me.  There’s a LOT of soldering going on in there!

2014-07-20 17.25.04

(more…)

-

Retro Challenge – New IDEa

just a quick update about my Z80 development environment.

If you look down a couple of blogs, you’ll see that I found an online Z80 emulator and I’d written a couple of bits that executed in it, so I was going to do my Z80 learning and development on that.  However, there were two issues.  The first being that it didn’t run on Chrome on my Linux PC at home (but did on Chrome on Windows at work).  The second issue is that it isn’t a Z80 emulator, it’s a 8080 emulator.  I didn’t think this would be a problem as they pretty much run the same instruction set, although the 8080 has a sub-set of the Z80 (well, technically, as the 8080 came first, the Z80 has an expanded instruction set), and I quite quickly came across an instruction that wasn’t supported.  Bugger!  That’s messed up that plan.

Then I remembered I have Fuse which is a ZX Spectrum emulator running on my Linux PC.  There are oodles of menus and options which I’ve never looked at, but thought it worth a poke (no pun intended) about with.

Screenshot from 2014-07-16 22:31:09 (more…)

-

Retro Challenge – Half-time Catch-up

We’re at the halfway mark of the Retro Challenge, and there’s a slight lull in activity, so this seems like a good chance to catch up on what’s been done so far, and what’s still to come.

Firstly, a quick review of the challenge I set myself; write my name in LED lights.  These must, however, be controlled by a Z80 computer, which I’ve got to design and build myself, and written in assembly language which I need to learn.

Well, the start of the challenge saw me dive headlong in to KiCad, learning some of the intricacies of printed circuit board layout.  I’d used KiCad for a couple of little projects before, but certainly wouldn’t have described myself as competent.  I’m still not a master of it, but I’m a lot more familiar with it than I was.

I split my breadboard based Z80 down in to several modules, each of which will plug in to a Veroboard backplane.  6 of these have been designed and sent off for manufacture which will give me a basic Z80 computer that I can use via a terminal emulator.  The boards are;

  • CPU
  • Eprom (for BASIC eprom)
  • Eprom (for my Z80 code)
  • RAM
  • Clock
  • Serial I/O

2014-07-04 18.58.00 (more…)

-

Retro Challenge – A Glitch In The Matrix

I knew there would be some stumbling blocks with this Retro Challenge, but, hey, it wouldn’t be a challenge if everything was just nice and simple.  However, I seem to be beset by little stupid technical issues that aren’t necessarily retro in nature.

However, the fact that you’re reading this does at least mean that my blog is working again!  I ran some updates last week, and it caused some issues with a plugin meaning I had no way of adding, editing or modifying any posts.  I’ve now got that tracked down to the Poll plugin and disabled it.  So, yay, I’m back!

So, part of this challenge is to use LEDs, and the little 8×8 matrix modules I found seem ideal.  I had initially intended to design a PCB to mount a bunch of these on, but due to time constraints, it was looking very unlikely I’d get them designed, ordered, manufactured and delivered by the end of the month, let alone time for testing.  So I decided to go Old Skool, and do this part on a breadboard.  Well, 2 breadboards, as they each need a driver chip.  Although, it’s actually 3 breadboards, as 2 aren’t quite big enough.  Not to mention the other breadboard with the supporting circuitry on.  I made a start on this last night;

2014-07-14 20.50.03

 

(more…)

-

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

(more…)

-

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…)

-

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…)

-

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…)

-

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…)

page 3 of 4