Thursday, July 19, 2012

8085 Monitor Code and Other Distractions

I've been working on an 8085 microprocessor project for about 3 years now. It started with a simple circuit on a breadboard, moved to my HP Logic Lab, where it became a real computer, then got built into a permanent version on a prototyping PC board.

I've been documenting the thing since it moved to the Logic Lab on my web site, posting how-to articles on building both versions (the hardware is identical, only the construction method is different), as well as software to control the hardware.

Where I've come up short is putting together a sort of unified OS for the system online that allows software to be developed right on the system itself, as well as any high level languages. I've been writing lots of software for my own use with the system, mostly hand-coded using my assembly coding forms and my 8085 Pocket Reference Card. But I keep either getting distracted from or otherwise dodging the job of integrating all the software bits I've already got into a simple "monitor" program (sort of a mini-OS for machine language) for the system.

Part of it is the usual life distractions. I've been sitting next to a wild fire this past week, for example. And then I've got lots of other electronic toys I like to spend some time with. Each one has its own appeal.

Before the fire, and a bit during (when I was taking a break from cutting ever more brush around my property) I've gotten back to work on putting it together. The biggest part is the part that reads the keyboard, determines the current system state, and dispatches keystrokes and execution to the right place. All the hardware interfaces are already in place, most of the basic system routines are in place (timing/delays/string handling), etc. So the "glue" is pretty much all that's needed. And I got it about halfway done before the fire started, I'm writing the code that actually takes actions for each mode, or simply hands over the necessary info to user apps running on the system.

So, if I can get time away from deck repairs on my house this weekend (now that it looks like it's unlikely to burn down or that I get evacuated), I'll be trying to wrap up and test that code.

Small Thing, Big Obstacle

The other thing I'm looking forward to is replacing some of the switches I put on the MAG-85. I put in switches for various interrupts about two years ago, and the switches themselves turned out to bounce and make so much noise that I've given up on them. No amount of debouncing, hardware or software, within reason has made them reliable. I'd hate to have someone else construct a MAG-85 and have to deal with this. It's been a thorn in my side ever since I added them, and took a lot of the fun out of the permanent hardware project for me (on the breadboard version, I used some old keyswitches out of a knackered Mac Plus keyboard, they worked great with only the most minimal hardware debounce. But I figured I could hardly specify 25 year old keyswitches in a project that others might want to build.

I'm expecting a shipment of a bunch of different switches tomorrow that I can test and select from to replace the awful switches I have now. So I can put that behind me (and probably re-simplify the circuit to take out a bunch of the extra parts I put in to try to deal with the noise on these switches.)

Frankly, the old switches are something I'd about hesitate to use in a doorbell circuit, never mind real electronics.

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