I just refreshed / restored an original Commodore PET. It spent its working years in the Richmond School District here in the San Francisco Bay Area. I rescued it the day before it was to become landfill. Now I guess it is just decor. It was picked up at the Albany Computer Services liquidation on May 7, 2011 near Berkeley and in pretty bad shape... 34 years of grime; dents, scratches and gouges; rotten cassette belts; overheating chips; one or more bad ROMs; broken fuse holder; etc. It would run okay for a few minutes then lock up. I went through about three monitors before I found a good one. The whole thing has been completely taken apart, cleaned, painted and put back together.
Today its got all new ROMs -- upgraded to v2 so the IEEE-488 routines work now. All that work was done by Matthew D'Asaro. His adapters are capable of replacing a single MOS Technologies MPS6540 ROM chip with a 2716 ROM chip programmed with the code. It is an exact electrical replacement for a 6540 (except that they do not require a clock signal.) All five chip select lines are fully functional. They use only parts that were available in 1977 and so they do not look out of place in a PET.
All the RAM has also been replaced. There are lots of spare chips now to hopefully keep it operational for another 30+ years.
Interior Photos
PETUNIA is a 4-voice music system which delivers "Chamberlin type" (see "BYTE" SEPTEMBER, 1977) music through an amplifier-speaker system. The PETUNIA board plugs into the parallel user port and the 2nd cassette interface as shown in the exterior photos above. Polyhponic high quality sound - based on HAL Chamberlin's sound projects. 8-bit DAC.
PET BEEPER, on the other hand, will automatically beep when a file header is found or written, and will also beep when a program is finished being loaded or saved. It used to take a long time to load and save programs with cassette tapes, and people got tired of watching the screen waiting for READY to appear. The BEEPER let people focus on other activities during these times while continuing to monitor their computer.
PET BEEPER can also beep at other times -- like under program control for adding emphasis and game effects to programs and for use in interactive audible feedback applications. It has a volume control for adjusting the level of the beep to one's own ear.
The red wire hanging off the BEEPER in the interior photos above is +5v DC to hook up a video mixer (adapter) which allows you to connect a standard composite video monitor. Repeatedly turning on and off the internal monitor in a PET can damage it, so they recommend using one of these adapters or similar when troubleshooting.
I thought about seeing if I could sell this computer for its original price: $795. (That was $2,826.66 in 2011 dollars.) I may just hang on to it.
The guy that designed it was the same guy that designed its CPU (the 6502) in 1975. It has been used in about everything including Apple products. He is still around and people like to hear him tell stories from those early days of home computing.
The computer's name was based off of the PET rock that was popular at the time. The 2001 model number was inspired from the title of Stanley Kubrick movie of the same name.
The CEO of commodore wanted them to use that ridiculous keyboard because he thought of computers as big calculators and Commodore was in the calculator business then. The case was made out of the same materials as a filing cabinet and the reason is because they owned a company up in Canada that fabricated office equipment and getting them to design a case was cheaper than all other alternatives. This thing is sturdier than the sheet metal on my car. I'm thinking about pin striping it!
Customers had to pre-pay and wait up to 1/2 year to receive their computer due to demand.
The BASIC language contained in it was written by Bill Gates himself, when Microsoft was just starting up, and sold to Commodore for a flat fee of $10,000. He later wrote that it wasn't a smart move in hindsight.
A lot of the very early chips were white ceramic with gold pins. I found one of those and saved it. It still works. You can see it in the interior photos above. (Second photo from the right on the bottom row next to the video mixer photo.) It is a white rectangle with a square gold label. It is from 1978 and contains some of the Bill Gates code. If you type WAIT 6502,1 it will print MICROSOFT! on the screen. Mr. Gates added that Easer Egg after a fight with one day with the CEO of Commodore.
You can't really do anything with this computer by today's standards. It is about as basic as you can get -- but state-of-the-art for '77.
I've got an MSD SD-1 disk drive hooked up to it and about 18 disks worth of programs downloaded from the Internet. I've typed a couple things in manually and may do a few more. There are many books and detail documents online pertaining to this computer. For example, the joystick drawing to the right is from the PET Users Group Newsletter; Volume 0, Number 3 and published by the University of California at Berekely's Lawrence Hall of Science under the Computer Project. I have validated that these instructions work.
Another hack is to add a reset switch, so I consulted my local Commodore guru, Mike N. about this. The system resets when /RES on the 6502 is pulled low. One way would be connect a switch from Vss to /RES with a momentary button. It works okay, but is not recommend because the switch bounces. "We ideally want a clean reset pulse," he explained.
The reset pulse on the PETs is generated by a 555 Timer configured as a "monostable multivibrator" (one-shot). To add a reset button you just have to momentarily ground the 555's trigger input (pin 2).
As pictured to the left, the 555 should be easy to find on your board since such a small (8-pin) chip. Please verify the connections against your board and the schematics before hooking it up. The dimple in the top of the chip marks pin 1. Space is cramped in this area. I found that the easiest way to grab pin 2 is actually at the capacitor in front of the IC with a clip to the base as shown (black clip).
What is more, in, "COMPUTE! ISSUE 1 / FALL 1979 / PAGE 89," Commodore uber-guru, Jim Butterfield, wrote that on upgrade ROMs you can come out of a hard crash with memory preserved. The trick is to set the diagnostic sense pin to ground then reset the computer. The processor will re-awaken in the Machine Language Monitor with memory preserved.
The diagnostic sense pin is #5 on the PET's User Port. Momentarily ground it at the same time you are momentarily grounding pin 2 on the 555 Timer and that is what he is talking about.
Jim continues, "...You're not yet out of the woods. Type a semicolon followed by RETURN; PET will respond with a question mark. Now move the cursor back to your register display line, and change the Stack Pointer (SP) value from 01 to F8. This strange procedure is important: you must follow it exactly. Once you've done so, you're clear. You may return to Basic with an X if you like or proceed in the MLM."