've long been thinking about a version two RC2014 LED matrix module. I've had a matrix with a MAX 7219 on a module. It's a nice enhancement.
But there's only so much you can do with a single-colour LED array right? Wouldn't it be cool to have RGB LEDs? At Liverpool MakeFest I saw a wall-sized ping-pong ball NeoPixel display and picked up some NeoPixels with the intention of making one. Possibly driven by my RC2014.
I enjoy learning about protocols and have had some SPI devices working with the RC2014 - bit-banging SPI works really well because it doesn't care about timing.
NeoPixels really do care about timing though. From Adafruit's web page about their 8x8 NeoPixel matrix:
If there's one thing I want to get across in this blog post, it's don't just accept what you're told. Question everything. Learn about what's going on and find out why you're being told something isn't possible. Get creative with workarounds.
I've learned a lot about Z80 timings during this project. I had assumed that because the clock speed I'm using (7.3MHz) was close to the speed required, that I'd be able to drive a line high and low at close to that speed, but no. An 'out' instruction, for example, takes a whopping 11 or 12 clock cycles.
So a little bit of extra hardware is required. An interface if you will. And some careful programming. This article was a huge help. It reinforces my message about questioning what you're told. Some parts of the timing are very tight. Some are really flexible.
So for this solution (actually the one that worked after a few that didn't) there's not much required. Besides the '138 for decoding the port address (I'm using port 3 - which seems not to clash with anything else on the RC2014, Spectrum or Minstrel 4th) there are just a couple of logic chips and passives here.
The first time I had a program switching on a pixel was a great day!
Once I'd got the hardware working reliably, and some of the fundamental code working, then it's very easy and fun to write a few demos. (See video further down the page.)
The breadboard wasn't terribly robust (I tend to buy cheap ones)
.. and so a pcb was the next logical step. The tall one (for the Adafruit 8x8 matrix) went through a couple of versions before I added the standard-sized one.
In both cases there are headers for daisy-chaining more pixels (and here we're back to my ping-pong ball display, which is now closer to being a reality) and you can include or bypass whatever pixels are on the board. The very clever protocol means that you simply daisy-chain your pixels and address them by index number in your code. Once a pixel has received 24 bits of data, it simply passes any further data to the next one along.
All of these pixels follow the WS2812B protocol. I've now bought a bunch of pixels in various formats from sources ranging from reputable to less reputable and they all work. The only minor thing is that most are GRB, some are RGB, which requires a little tweak to the code depending on which you're using. (I have some WRGB but haven't tried working with those yet.)
Here's a video in which I talk about the project and show off a whole bunch of demos that I've written - some in BASIC (using a blob of machine code for the low-level stuff) some in assembly but most in C.
So the next challenge was to see whether this could be made to work with a Spectrum. This has the same Z80 processor but it runs at around half the speed of the RC2014. Because of the way my adaptor board works, and again exploiting that flexibility in some parts of the timing, I have been able to make it work. It took a tweak to component values on the adaptor, and a tweak to the code too. But in principle it's using the same adaptor board, and working in the same way. Thanks to Z88dk which can target RC2014 and ZX Spectrum, I've easily been able to build my existing C and Assembly demos for Speccy.
A while ago I made this MIDI module for RC2014: It works but a better design would have its own serial chip and port decoding. As it is, it provides the MIDI interface and a clock signal for the second SIO2 serial port. This means that it requires a little setting up and will only work for RC2014s with an SIO2 (and port B not already used). I think people might reasonably expect it to be plug-and-play and self-contained, ie do all the serial itself. My challenge to myself is to: learn how to connect a serial chip (probably 68B50 ACIA) to receive the incoming MIDI and to serialise outgoing MIDI design the module, including the port decoding write a library so that it can easily be used on any RC2014. Potential applications include a MIDI sequencer and using incoming MIDI to trigger notes on the AY or SID sound chips. Entering the Retro Challenge 2024 (aka RC2024/10) has given me an incentive to get on with this! I'm happy to see several more entries in the RC2014 catego...
Each year I've been trying to get more creative with ideas for Spencer's birthday cake. The plan this year was to incorporate LEDs in place of candles. I eventually settled on an Altair / IMSAI / PDP -style computer since those are the type of computers that inspired his RC2014. The IMSAI 8080 has the most colourful switches as well as a name that I could twist. The thought that it could show randomly flashing lights (as if the computer were running) and that it could also play a game of 'kill the bit' was very appealing. A plan formed to use a capacitive touch pad on the cake itself. The first job is to bake the fruitcake. I often use a 7" square tin and one of those cut in half and rearranged makes a cake of suitable proportions. Even after taking a slice off the faces to make them nice and square, there are still some rounded corners, so after putting on the marzipan, I used more marzipan as a filler to flatten the whole thing. Even though I wanted to end up w...
For me, graphics capability is essential for an 8-bit computer. My graphics chip of choice for the RC2014 is the very capable TMS9918A. It has 15 colours, sprites, several modes and a max resolution of 256x192. It makes arcade-style games possible, such as Tut-Tut above. I enjoy simply displaying images and have a bunch on my CF card (my 'hard drive') and have written image viewer and slideshow apps to display them. Some useful links: Convert9918 Tutorial of Convert9918's settings Multipaint J B Langston's TMS9918A video module my own TMSEMU video module my respository of TMS9918A software, games and .s2/.sc3 images Image conversion I did dabble in writing my own utility to convert .png images but then settled on the Multipaint app which can open a png in a MSX 'screen 2', allow you to tidy it up with paint tools and save as a .sc2 file. (An sc2 file is little more than a video-memory dump and so it's easy to blast that back into vram to display the image....
Comments
Post a Comment