Monday, January 3, 2011

Retrochallenge 2011 Winter Warmup!

I'm getting started on my Retrochallenge Winter Warmup 2011 project! Here is the description and some more details...

A while back, a friend gave me a PET 2001-8N. It's in really nice condition. The -8N means 8K of RAM (and a standard sized keyboard), so it's not a powerhouse - but it is among the first models of computers produced by Commodore. I have the accompanying tape drive - a C2N Datasette. But I have to admit, I've wanted a disk drive.

My PET is not the first model produced by Commodore - that honor would go to the smaller keyboard PET 2001 with the built-in datasette. (This is, of course, if you don't count the KIM-1 SBC, which was produced by MOS Technology prior to the Commodore acquisition.) However, my 2001-8N does have the correct ROMs to support a disk drive. So when the opportunity came up to get an SFD-1001, I jumped at the chance. It needed about $30 worth of repairs, but now it's up and running, and refurbished.

The SFD-1001 is an interesting device. It can store 1 MB on a single floppy disk. It is supposed to use "quad density" media, but even back in the day, this was pretty rare and expensive. So people figured out that you could use standard double-density media, and it would mostly work. That's what I plan to do. The SFD-1001 looks much like a standard Commodore 1541, but it has an IEEE-488 interface. And, as it turns out, I don't have an IEEE-488 cable. I could buy one, but I already have the pieces, so I'm going to try building one. Which brings me to my project:

Step 1: Build the cable

The PET user port is the same style connection as the VIC-20/C64/C128 user port. The pinouts are not all the same, but the flat-edge connector style is identical. As it turns out, the IEEE-488 connection on the PET is also the same style connector - it just has the flat-edge "notch" at a different location. If you're using a non-keyed connector, you can use a user-port connector for the PET side of the cable. I have a solder-style user-port connector, so I'm set on that end.

The other side of the cable is more of a problem. The disk drive end of the cable requires a male 24-pin Amphenol plug. I do have one; however, I'm going to have to harvest it from a non-working IEEE-488 adapter for the C64. It is a difficult decision to "snip" this cable from the adapter; however, the adapter is broken, and I don't have the facilities or inclination to fix it. So, the Amphenol connector and attached ribbon cable will be "re-purposed".

I have to sketch out the pinouts for both sides of the cable, then get out my wire strippers, soldering iron, multimeter, and make it happen.

Here's the rest (details coming in later posts):

Step 2: Test the cable by formatting a disk, then saving/loading a program.

Step 3: Get some software from the Internet, get it to the PET, then get it on the disk drive.

Step 4: (Extra credit) Figure out if it's possible to "chain" BASIC programs, so that an 8K PET can run some programs that are slightly more sophisticated.

Off I go! Pictures to come shortly!

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