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AT&T UNIX PC enthusiasts out there?

agentb

agentb

Experienced Member
Joined
Apr 22, 2021
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366
Location
Philly, USA
The AT&T UNIX PC aka PC 7300 aka 3b1 is one of my favorite UNIX machines. Any other fans/owners out there?

Last year I got into playing around with one virtually with Phil Pemberton's FreeBee emulator (https://github.com/philpem/freebee). And then I added some enhancements along the way which was a lot of fun learning more about the details of the hardware. Well just recently firebirdta84 hooked me up with some real deal hardware which has been awesome! AJ helped setup David Gesswein's MFM emulator in the machine to get me up and running. There's no floppy so I'm going to see if I can get a gotek working with it, who knows! The UNIX PC FAQ does say that a 720k 3.5" floppy can be supported, but not a 1.44" for some reason. But hoping to just emulate the standard 400k 3b1 floppy.

I am also lacking a 3b1 mouse so I've been working on a ps2 mouse to 3b1 converter which I've got prototyped. Now trying to figure out a proper hardware design for the converter. That said, does anyone else have the need for a ps2 mouse or keyboard converter for their 3b1? I could probably add keyboard support too if anyone was interested. I know AJ was interested in a mouse converter.

Anyway, if you have any other fun anecdotes about the AT&T UNIX PC, please share!
 
Haha, I just happened to come across that picture yesterday of your wife with the 3b1 at VCF East -- I thought that was really cool. I'm in fact using your VCF image right now on your MFM emulator (that AJ built), and I also use that image with FreeBee! Thanks so much for putting it together. It's come in handy for me, and also is a great resource for anyone who wants to try out FreeBee. When I first played around with FreeBee, you needed to do the full OS install and there is an emulator glitch where the install process can hang when it gets to "setting up screen".

I'll have to check out that story of the dungeon port. 8-)
 
I have three, so you could say I'm in to them. Along the way I accumulated an expansion memory board, PC emulation board (8086), expansion chassis, tape drive and one serious unicorn: the ethernet adapter. Very cool machines with classic styling.
 
shirsch said:
Along the way I accumulated an expansion memory board, PC emulation board (8086), expansion chassis, tape drive and one serious unicorn: the ethernet adapter. Very cool machines with classic styling.
Click to expand...

Ahh yes, the fabled Ethernet card! I would love to get my hands on one of them some day. I hear the TCP/IP stack isn't great but it's gotta be better than not having one. I have heard of a number of people with the DOS card, I wouldn't have guessed that would have been as popular as it seems it may have been. And the expansion chassis, wow -- I have read of it but never saw one or even a pic of one. It's impressive they even made such a thing. I would have guessed 3 slots would have been sufficient. I hope to get a RAM card some day too, but I've got 1MB for now.
 
Today I used the serial port and a null modem cable to xmodem (“umodem -rb”) over a file, fortunately worked without an issue. That file was an interesting one which was the vidpal emulator. It’s a driver that lets you write directly to VRAM. Easy to compile and install and seemed to work. I’m interested in being able to write to VRAM as it’s straightforward and I don’t have to learn the “proper” way you’d otherwise do it. There’s overhead for sure but don’t think I want to mess with a hardware workaround at this point like the original Vidpal mod. Anyway if you are interested the vidpal emulator is here: http://www.unixpc.org/ftp.funet.fi/pub/archive/comp.sources.3b1/volume1/vidpal-em/
 
Question: For some reason I ended up with a 3B1 / 7300 EIA + memory board with no memory (or support logic) populated. I cannot find any mention of an EIA (serial) only version of this product. Has anyone else seen such a board? I'm sorely tempted to build it up for my extra 3B1.
 
Wikipedia says there were dual EIA cards. Maybe for the dual EIA they just used the RAM/EIA card but without memory populated? From Wikipedia:
  • RAM card could be added using 512 KB RAM or 2 MB RAM cards, up to a maximum of 4 MB (2 MB on the motherboard and 2 MB on expansion cards).
  • EIA/RAM combo cards contained extra RAM (512 KB, 1 MB, or 1.5 MB) and two RS-232serial ports.
  • Dual EIA port card
 
I learn something new every day... After digging through the AT&T docs I discovered that they indeed offered an EIA-only version of the RAM/Serial board! Just ordered a bunch of chips and sockets and plan to populate it out to 1.5M for use in my backup machine. Fortunately, the delay line is already there and no programmable parts are required. Clearing and resoldering 500+ holes will probably be a bit tedious, however.
 
Whoa, cool project to get that extra 1.5MB -- a lot of soldering but will be great to have the extra RAM!
 
Heh. I'm warming up for the exercise by performing the ICUS II hard disk mod. Got most of the preliminary work finished and will start adding the 18-odd jumper wires tomorrow. Couldn't find a JEDEC file for the PAL16R4, unfortunately. After a brief learning experience I was able to compile the EQN source using OpalJr under DosBox. If anyone needs the JEDEC, I'll be glad to post it after I verify a working system.
 
Implementing the ICUS II "P5.1" mod is not my idea of fun, but it was straightforward and seems to work. Attached is the JEDEC file I used to program a PAL16R4CN.
 

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I have wanted one since I played with one at ElekTek way back... I used to come to the store just to play with it as a kid. Alas, I have not been able to find one since then. Very jealous of all the lucky owners here...
 
shirsch said:
Implementing the ICUS II "P5.1" mod is not my idea of fun, but it was straightforward and seems to work. Attached is the JEDEC file I used to program a PAL16R4CN.
Click to expand...

Glad you got it working. This let’s you use a larger hard drive and a 2nd drive, right? Thanks for sharing the JEDEC file. The VIDPAL mod is the one I’m most interested in as it allows you to draw directly to video memory. There are software mods but they involve additional overhead. The VIDPAL mod just fakes the supervisor line on the CPU so that an exception isn’t triggered when you attempt to write to VRAM.
 
polbit said:
I have wanted one
Click to expand...

if you have a chance, check out the FreeBee emulator. That’s what got me back into the UNIX PC! I’ve recently begun working on the MAME driver for the UNIX PC. I was having some trouble getting the floppy drive working but seem to have figured that out. Now I’m having an issue with the CPU attempting to read from the 6850 keyboard controller. A lot of work to do on the driver but I’d like to see it emulated in MAME.
 
polbit said:
I have wanted one since I played with one at ElekTek way back... I used to come to the store just to play with it as a kid. Alas, I have not been able to find one since then. Very jealous of all the lucky owners here...
Click to expand...

Things changed over the past couple of decades, for sure. Folks were giving these away during the 90s, which is how I came upon my first two units. Then someone found a bunch of NOS 7300s in a warehouse somewhere in the Midwest and I was able to pickup a brand new, sealed system for $150. Today, I'm sure they are bringing stupid prices. Couldn't even find one on eBay. Over the earlier years I was able to accumulate one of the very rare ethernet adapters, tape drive w/ interface, expansion box and a DOS-73 board. Somewhere I have a StarLAN board, but have never used it.
 
agentb said:
Glad you got it working. This let’s you use a larger hard drive and a 2nd drive, right? Thanks for sharing the JEDEC file. The VIDPAL mod is the one I’m most interested in as it allows you to draw directly to video memory. There are software mods but they involve additional overhead. The VIDPAL mod just fakes the supervisor line on the CPU so that an exception isn’t triggered when you attempt to write to VRAM.
Click to expand...

Yes, by also adding a WDC2010 controller it will support disk geometries up to 1400 cylinders and 16 heads. Since no physical hard drive with that many heads ever existed you need an mfmemu or DREM (I'm using the emu currently).

I would love to add a VIDPAL, but the developer is no longer active and never saw fit to release the device equations and schematic. If anyone has a VIDPAL, please try to read out the fuse map?
 
I have two here. Both powered up in 2020, one was able to boot the diagnostic floppy before I ran out of time to play with them. I've got a couple MFM emulators on hand for them, as neither has a working HDD.

I think I've got the tape controller, DOS card, StarLAN, 3rd party memory card, and a couple EIA cards. In hopes of doing better than the serial ports, I picked up a box of StarLAN 1 ISA cards, but haven't done anything with them yet, either.
 
smj said:
I have two here. Both powered up in 2020, one was able to boot the diagnostic floppy before I ran out of time to play with them. I've got a couple MFM emulators on hand for them, as neither has a working HDD.

I think I've got the tape controller, DOS card, StarLAN, 3rd party memory card, and a couple EIA cards. In hopes of doing better than the serial ports, I picked up a box of StarLAN 1 ISA cards, but haven't done anything with them yet, either.
Click to expand...
I'm using one of David Gesswein's MFM emulators in my UNIX PC. Works great. Certainly prefer doing that to a physical HD. Though I suppose I do miss the coffee grinder noise.

Oh man, that's a lot of the expansion cards, nice. Do you happen to have the unicorn Ethernet card? Do you know of who makes the 3rd party memory card? I wasn't aware of any 3rd party cards so that would be interesting to know about.
 
smj said:
I have two here. Both powered up in 2020, one was able to boot the diagnostic floppy before I ran out of time to play with them. I've got a couple MFM emulators on hand for them, as neither has a working HDD.

I think I've got the tape controller, DOS card, StarLAN, 3rd party memory card, and a couple EIA cards. In hopes of doing better than the serial ports, I picked up a box of StarLAN 1 ISA cards, but haven't done anything with them yet, either.
Click to expand...

Back when I started collecting vintage machines (early 90s) it was much easier to find AT&T hardware. I ended up with (2) hump-backed 7300s and one wedge - the latter was NOS in the original box. Also have ethernet card, Starlan board, tape controller, official AT&T tape drive, expansion chassis, DOS73 and - like you - a bunch of ISA StarLan boards. Just resurrected the last of them, which needed serious cleaning and replacement of a thermally intermittent CPU. I made the ICUS II mod and installed a Gesswein mfmemu to emulate a pair of 1400 cyl, 16 head drives. Lots of space to spare now.

After seeing agentb's 3B1mouse project, coded up the same function on a RaspberryPi Pico to sub for the missing mouse on my third unit. I currently have a mini-Pico device (Qt from adafruit) on the way for the next project: Installing the mouse protocol converter inside the shell of a Logitech PS/2 mouse. These are very interesting and fun machines to work with and were way ahead of their time.

I have a few AT&T tape drive mechanisms picked up at a swap meet. Not sure what their status is, but if anyone is interested I can dig them out and test. Might help someone with tape drive controller and no drive. Just a matter of mounting in a box with a power supply and building a cable.

Almost forgot: I was able to populate an EIA/RAM board that was manufactured without the memory. A tedious job that involved clearing solder from 500+ holes and mounting 60+ sockets and chips. But, it can be done and works great.
 
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