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View Full Version : Got out my old PET 4032 ... some help please?



gsteemso
January 18th, 2009, 06:47 PM
Hi all!

Just retrieved the rest of my retrocomputing collection from my parents' place in Canada, and was delighted to discover that the PET still works. On examination, it has something to the effect of "80 column mainboard" written on the PCB, but it only shows a Fat 40 screen. (Apparently, at least -- Jim Butterfield's machine language book says you can distinguish a Fat 40 from a regular 40 by the way the cursor keys autorepeat. This one's do, so...)

The ROMs are in 5 chips. One is socketed and the others are not; the socketed one has a different part number than the others. (The soldered-on ones are 901465-20 through 901465-23; the socketed one is 901499-01.) There are also two sockets for user ROMS; one is empty and the other contains an unlabelled mystery EPROM with the window taped over. What's up with the socketed system ROM not matching the other four? Is there any way to tell what's on the user-ROM thingy?

This thing has a ridiculous number of jumper posts and expansion headers in it. There are two unpopulated jumper post sockets, two 50-pin ribbon cable connections which appear to be for system expansion of some description, the user-port, IEEE-488 and cassette-port edge connectors along the back of the board, and what appears to be a SECOND cassette edge connector on the right-hand side of the board near the usual one in the back corner. The two 50-pin headers and the, apparently, second cassette connector are behind a metal plate screwed to the case. What can I connect to all of these things and is there any reason to bother? I understand I can update the thing to 80 columns by closing some jumpers. Which ones and what else do I need to do?

Any help or advice you may offer would be gratefully received!

tezza
January 19th, 2009, 03:05 PM
What's up with the socketed system ROM not matching the other four?

Could it be that the ROM was replaced in the past? Hence the socket and the different numbers.




This thing has a ridiculous number of jumper posts and expansion headers in it. There are two unpopulated jumper post sockets, two 50-pin ribbon cable connections which appear to be for system expansion of some description, the user-port, IEEE-488 and cassette-port edge connectors along the back of the board, and what appears to be a SECOND cassette edge connector on the right-hand side of the board near the usual one in the back corner. The two 50-pin headers and the, apparently, second cassette connector are behind a metal plate screwed to the case.

Yep. Same with my 3032. Phillip Avery (pavery in this forum) and I speculated on the reasons for all those unconnected connectors and edges when we were examining the board. I have a Pet user manual which does explain what goes where as far as the ones accessible from outside the case are concerned. The two 50-pin ribbon cable connections are for system expansion and the user connection, IEEE connection and cassette connection are all documented. However, I haven't a clue what the others do. I'd also be interested in finding out.

Tez

tezza
January 19th, 2009, 03:23 PM
More specifically, I'm wondering about the purpose of the connectors indicated by the red arrows in this PET 3032 schematic.

http://classic-computers.org.nz/blog/images/2009-01-19-pet-3032-mystery-connectors.jpg


Gsteemso, you mentioned "a SECOND cassette edge connector on the right-hand side of the board near the usual one in the back corner". On my board, it's on the front left hand side (looking at the board from the front)? Is this what you meant, or are our boards very different? My right hand back part of the board contains the pins for the expansion bus.

Tez

gsteemso
January 19th, 2009, 04:34 PM
Since my original post I have learned that there are in fact two cassette connectors, and the socketed system ROM is the one that varies between PAL and NTSC boards. (Why they care one way or another, given that there is no video out signal, I could not begin to guess.) I'm still in the dark about the user ROMs, the jumpers inside and the details of interfacing to the expansion headers.

gsteemso
January 19th, 2009, 04:59 PM
More specifically, I'm wondering about the purpose of the connectors indicated by the red arrows in this PET 3032 schematic.

http://classic-computers.org.nz/blog/images/2009-01-19-pet-3032-mystery-connectors.jpg

The one on the left is the second cassette connector. The other two are the jumper pads.


Gsteemso, you mentioned "a SECOND cassette edge connector on the right-hand side of the board near the usual one in the back corner". On my board, it's on the front left hand side (looking at the board from the front)? Is this what you meant, or are our boards very different? My right hand back part of the board contains the pins for the expansion bus.

The boards are completely different. The chips on mine are oriented 90 degrees away from where they are on yours, and the second cassette connector is indeed at the opposite corner of the case.

I will see if I can post a picture.

MikeS
January 19th, 2009, 05:20 PM
The socketed ROM is probably the character generator which would be different for different countries and models. The two rows of jumpers more or less in the middle of the board select 40 or 80 columns; I have the settings but can't find them at the moment, but they're out there somewhere on the Web.

To find out what's in the unlabelled EPROM, check which socket it's in and then SYS the base address of that socket; it may identify itself. Otherwise you'd have to look through it to see if there's any identifying text anywhere.

They all had two cassette ports, but the second one is not fully functional on the later BASIC4 models. The 2001 models like Tezza's have it on the side instead of in front.

Tezza: if you check, you'll probably find that those two connectors are auxiliary power connectors J10 & J11. See the power supply schematic.


m

carlsson
January 19th, 2009, 11:46 PM
Yes, J10 and J11 are for auxiliary power, but I don't know when or why they would be used. Fortunately the video cable is keyed so it won't fit into either of these by mistake.

901465-20 = PET 4032/8032 Basic V4 (4K 1/3)
901465-21 = PET 4032/8032 Basic V4 (4K 2/3)
901465-22 = PET 4032/8032 Kernel (4K)
901465-23 = PET 4032/8032 Basic V4 (4K 3/3)
901499-01 = PET 4032 Editor V4 60 Hz (petedit-4-40-n-60Hz)

I'm not sure if the 901499-01 is for graphical or business keyboard. You will probably see that on your keyboard which layout it has.

The character generator would be 901447-10 or so.

By the way, the unknown EPROM could probably be removed from its socket and read in an EPROM programmer if you have one handy. Otherwise, it should map into either of $9000 or $A000. Try SYS 36864 or SYS 40960. It is possible the code starts a few bytes into the chip though.

tezza
January 20th, 2009, 12:32 AM
Tezza: if you check, you'll probably find that those two connectors are auxiliary power connectors J10 & J11. See the power supply schematic.


Ok, thanks.

Tez

MikeS
January 29th, 2009, 08:35 AM
Well, in the meantime Tezza has figured out how to dump the ROMs without a programmer; you'd probably only need to list it to the screen a page at a time and hopefully you'd see some text that would give you a clue as to what that EPROM is if SYSing doesn't give you a sign-on message.

A big d'oh! Of course the removable ROM contains the stuff related to the graphics or business keyboard, and not the character generator as I thought; it's off by itself near the left front of the board. FWIW, UD7 (the socketed one) in my 8032 is a 90174-03.

Re changing a FAT40 to 80 columns, it's not a trivial job as there are quite a few etched jumpers that have to be cut and changed (unless your board is different from mine).
I installed jumpers on my board so I could change it back and forth, and I still have an almost-finished project to let me select 40 or 80 columns with a switch, waiting for me to dust it off and finish it (once I figure out again what I was doing 25-odd years ago).
I even have an external graphics keyboard for FAT40 mode.

If you really want to convert it I could probably come up with more info, although I'm sure I've seen it described on the 'Web somewhere

Anders? Have you run across that FAT40<>80col conversion info anywhere?

carlsson
January 29th, 2009, 09:25 AM
No, but I haven't looked neither. :-)

As for dumping ROMs, I wonder if the PET Kernels have routines for saving a memory block just like later VIC and C64 has. On a VIC-20 one could do as follows:

N$="FILE NAME"
SYS57809(N$),8,1:POKE193,start_lo:POKE194,start_hi
POKE780,193:POKE781,end_lo:POKE782,end_hi:SYS65496

The end address is one byte greater than the saved area.

Unfortunately I don't seem to find a replacement to the first routine which sets up a file name. Apart from browsing the disassembly yourself through the VICE monitor, this disassembly of 4.0 ROMs from a 8032 may be of some help:

http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/d/petdis

There are a lot of question marks though.

gsteemso
January 30th, 2009, 05:09 AM
As for dumping ROMs, I wonder if the PET Kernels have routines for saving a memory block just like later VIC and C64 has.

While that would let me get the ROM onto a 1541 disk, I have at present no way of getting that to a D64 image. Nice thought though. :-)

carlsson
January 30th, 2009, 11:27 AM
In theory you could save a memory block to tape as well. :)