So, it’s been a bit of a mixed bag this month with the 6809 computer. First of all, I have decided to do the SBC “properly” and use a single CPLD instead of two. With that goal in mind, I’ve ordered a few parts: XC9572 in PLCC84 (3 of) PLCC84 sockets (4 of) Initially I wanted to buy some XC95108s…. Read more »
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 »
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 »
It looks like my problems with the counter were down to the 555 timer. Replacing the crufty old 555 with an Atmel ATMega8 generating the clock signal caused the counter to start working properly. Here is the ABEL code: MODULE counter // Defined inputs CLOCK pin 1;RESET pin 2; // Defined outputs Q3..Q0 … Read more »
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 »
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 »
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 »
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 »
I haven’t had much time to work on my electronics projects lately, or write on this blog. The main reason being the arrival of a bouncing baby boy! So for once hobbies must take a back seat. If I’m lucky I will be able to write here about once a month. I have had a little time to work on… Read more »
To learn about I2C I have implemented a serial EEPROM programmer using the same AVR based ATMega8 as my old school paralled programmer. I2C, like SPI, is nice because all signalling between the microcontroller and the memory is along only a handful of wires. This also, at I2C speeds at least, makes it slower but adequate for many applications like… Read more »