Toggling an etch-a-sketch program into the Orton 3C

he Orton 3C is a minimal Z80 computer which can run using only three chips. As Spencer says, the design is "on the border of simplicity and genius". Credit to Karen Orton, who is sadly no longer with us.

It literally gets you hands-on with the Z80. Input of a program (or at least some kind of loader or serial program) is achieved 70s-style using switches connected to the address and data lines.

Spencer has taken Karen's design and implemented it using the RC2014 modular form-factor.

I love the bare-metal-ness of it but couldn't really justify buying one. One birthday later and here we are.

Without using a ROM, programs have to be short or you have to settle down for a lot of toggling. You soon feel the limitations of having no input/output - even a game of 'kill the bit' requires the front-panel i/o (which adds to the chip count). My initial programs involved animating those output LEDs.

Of course, any RC2014 module will work and so I tried a program to draw on an 8x8 matrix using two pots connected to my dual-analogue input module.

This program is a bit longer at around 100 bytes. It's still feasible to enter that with the switches (I'm becoming very conversant in binary!) but developing the program would have been tedious using just the 3C and hand-assembly. Initially I enjoyed using a RC2014 Classic with SCM to help with the assembly - just use the 'A' command to type in assembly and see the machine code. For this program, I used modern tools like a text editor and ZASM to develop, and my Classic to test. The 'D' command in SCM then gave me the disassembly that you can see in the picture above (I changed the $80xx references to $00xx although I don't think this is necessary with the Orton as it doesn't use A15 for addressing memory).

With that toggled in and checked, here it is running!

Comments

RC2024/10 - my entry

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...

IM53 8080 birthday cake

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...

New MSX graphics / sound / joystick module for RC2014 / RCBus

I'm impressed at what Les has packed onto this standard-sized module. It contains an FPGA replacement for the TMS9918A, a YM/AY sound module and joystick interface. The project is open-source and is here . In MSX terms this is the VDP (vidio display processor) and PSG (programmable sound generator), thus being an alternative for both the J B Langston TMS9918A video module and Ed Brindley's YM/AY sound module and adds two joystick ports to boot. All on a single module for RC2014 or compatible computers. There's no room for the d-sub joystick ports, so headers are provided so that these ribbon cables can be used. This is a neat solution for those wishing to take advantage of Les' MSX8 system , which loads most MSX rom files along with a modified MSX BIOS from CP/M on a ROMWBW RC2014. It is hard-wired to the MSX ports for the sound and video, so it won't be suitable for those wanting to run Colecovision ROMs, for example. I'm torn myself between the real TMS ...

New Stuff For Old Stuff :: Blog

Search This Blog