Category Archives: 6809

Design for a real Single Board Computer

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Though the previous PCB design was a vaguely useable computer, it required devices attached to an expansion port to be even moderately useful. A real Single Board Computer should be useful with just the single board. Combining a serial interface with an IDE interface should make the single PCB a computer in its own right, albeit one that only has… Read more »

A dissasembler and thoughts on a new core computer

First though, the integration of the seven segment display with the 6809 circuit. This turned out to be easier then expected. I added a bus driver component which replaces the counter to drive the mux, and in turn is driven (and drives) the databus. It also uses the read/write line and chip select control lines. The code for the bus driver is… Read more »

Adventures with Programmable Logic

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So I have received the following goodies: XC9572 x 3 (PLCC44) Platform Cable USB programmer (Model DLC9G) Some PLCC44 PCB sockets (through hole) PLCC44 to DIP44 converter for the breadboard PLCC extraction tool The XC9572 is a simple part, by modern programmable logic standards.  Not exactly capable of running a soft processor, the ‘9572 can still be used for one… Read more »

Hardware problems, XMODEM, and musings on programmable logic

In my last post I mentioned the problems I’ve been having with powering my computer. A multimeter on various ICs shows a big drop across the power pins on some of the ICs. The AY 3 8912, for instance, was getting only about 3V. I have worked around these problems by using an additional power source to counter the voltage… Read more »

Sound, and running programs from CF

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My investigation into MinixFS has revealed a nice and simple filesystem; probably the simplest filesystem which you could implement which has UNIX-like semantics.  It has inodes, permissions, and all the usual UNIX things, but (luckily for me) the first iteration of Minix-FS mostly uses 16 bit datatypes.  This means it is “fairly” easy to interpret the data structures which make… Read more »

SPI, IDE, and a PCB!

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It’s been another couple of months with no blog update. Busy busy. Anyway. In the few hours here and there (work lunch times, early morning, etc) I have managed a fair bit of progress. Firstly I’ve laid out the circuit again on some fresh breadboard slabs. I’m fairly sure the breadboard I used previously had some bad links, because the… Read more »

Monitor progress

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So far the monitor can do four things: Dump memory contents in hex and ASCII (d command) Write memory contents in hex (w command) Exit the monitor and run¬†arbitrary¬†code (e command) Show the registers as they were just before the monitor was reentered (r command) For ease of parsing each command is a single character. Monitors are generally implemented as… Read more »

Serial communications and the start of a “monitor”

“Monitors” were pouplar tools for debugging programs, along with other useful facilities. Some were also powerfull enough to be considered development environments in there own right. They provided the user with the ability to read memory content, modify memory contents and registers, execute external code, set breakpoints etc. Some had built in assemblers and dissasemblers. I will be writing my… Read more »