bitfixer

When collecting old computers, one issue that comes up from time to time is that you’re missing the one piece that you need to get the machine working. Or you have the piece and it’s beyond your ability to repair.
Keyboards are often the culprit. I’ve gotten a few machines with keyboards where the foam pads under the keys had deteriorated enough to prevent the key presses from registering. There are ways to restore the keyboards by getting new foam and laboriously cutting new pads for the keys, but sometimes you just want to get to it and play with your old computer without spending weeks shaving pieces of foam.

PS/2 keyboards are in plentiful supply and are fairly simple to interface with a micro controller. Often with a bit of work they can be adapted to work with a variety of old machines.

I recently saw a post on the Vintage Computer Forum from a guy in Vancouver who needed a keyboard adapter to use a PS/2 keyboard with a Fujitsu FM77AV40SX that was missing its original keyboard. I was interested in helping out, since I had some experience building a PS/2 to ASCII converter to use a digital group computer.
But one wrinkle was that I did not have access to the computer, so debugging any adapter would be a bit of a challenge.

Coming up is an account of an exercise in remote debugging using a protoboard with an AVR microcontroller, equipped with a serial port bootloader. It’s a thrill a minute I tell ya.
Hopefully this will help out collectors of Fujitsu computers who are missing their keyboards! Stay tuned for more..

Hi everyone,

Wanted to let you know about a new device for your Commodore PET: The PETvet!

Basically, the PETvet replaces all of the RAM and ROM in your PET using a single SRAM chip. Different ROM images are stored in the flash memory of an Atmel microcontroller, which pre-loads the ROM contents into the right place in memory before the CPU starts running.
You can also use the PETvet to view the memory contents of a running PET by dumping the contents over a serial port. This can be useful when debugging an ailing PET motherboard. It can also be used as a basic terminal output for a PET by viewing the contents of video RAM.

The PETvet is in the final stages of testing right now and will soon be available here as a kit or as a fully assembled unit. More details to come.

Finished another firmware update, this one allows you to use long file names when saving files on the PETdisk. So now you can save something like
SAVE “LONGFILENAME”,9
and it will work. Yippee!
Download the update on the PETdisk Technical page.

Check out the Plus Too over on the ‘Big Mess o’ Wires‘ site – it’s a hardware replica of a Mac Plus/Mac 512ke computer, built from an FPGA development board. A very impressive and exciting project!

Tezza, the creator of Tezza’s Classic Computers Blog, wrote an excellent article on the PETdisk. Check it out and his other postings as well.

That’s right, those fine podcasters of the Retrocomputing Roundtable(subscribe here) mentioned the PETdisk in their latest episode (show 16)! I am a fan of this podcast and of the individual podcasts of the hosts (Retrobits, 1mhz and the Classic Computing podcast) so it was a thrill to hear them talk about this little project on the interwebs. Thanks guys!

Hi there,

I’ve been working on an update for the PETdisk firmware which includes a bootloader to make future firmware updates simple. Now you will be able to update the firmware directly from the SD card – just copy a file onto the micro-SD card, put it into the PETdisk, and power on the PETdisk. Once the device finds a firmware update, it will automatically reprogram itself with the new code. This will even allow people to hack around on the firmware and try out changes themselves, without a programming cable. New PETdisk orders will include this update. I have changed the microcontroller in the PETdisk from an ATMega8 to an ATMega168, which has twice the program memory (16k as opposed to 8k).
In addition to the bootloader, the firmware upgrade will add support for wildcards, so commands like
LOAD “*”,9
or
LOAD “part*”,9
will now work.
Also the BASIC 4.0 DLOAD command is working, and I have fixed a bug which was preventing certain files with capital letters in the extension (“.PRG”) from loading properly.

It turns out that the serial programmer wasn’t working earlier because I was using it with a USB-Serial adapter, as I feared. However, when I dug out an old Sony laptop with a real serial port, it worked right away.
The PETdisk has most of the necessary connections for reprogramming brought out to the socket used by the SD card adapter, so it should be simple enough to connect a programmer to update the firmware. I will try this soon and let you know how it goes.
Also looking into AVR bootloaders so in the future the PETdisk firmware can be upgraded by just putting a file on the SD card.. watch for that also.

So far, no success in getting this simple DASA programmer to work.. Although I am using a USB-serial converter, which may be a problem. I will try again with a machine that has a true serial port.

Hi there,

Commodore PET enthusiasts out there might be interested in the PETdisk, which is a gadget I put together recently. It is a simple storage device for Commodore PETs which connects directly to the IEEE-488 port, and has a passthrough port so you can still connect other disk drives. Check it out at the PETdisk page.

For the PETdisk and other Atmel AVR projects, I normally use an STK500 programmer to program the microcontrollers, which works well – but I would like to try one of the simpler serial programmers to see how well they work. The immediate use of this would be to help those who already have a PETdisk to update their firmware when updates are available, but I am also generally interested in how simple the simplest possible serial programmer would be. I’ll let you know how it goes!