The ware for February, 2007 is shown below. Click on the picture for a much larger version.
I have had this ware since I was a wee lad, since I was probably just over a decade old, but to this day I don’t know what it does. I used to hang it over my Apple ][ in the basement where I would hack late into the night, writing assembly and BASIC code to control little hand-built robots and voice synthesizer cards. Clearly, the ware is from a DEC machine of some type, but I don’t know which one or what it does. I figured maybe this would be the right place to get answers to such mysteries from my youth, so here it is! Hopefully someone will be able to tell me what this relic did.
Judging from the bus and some of the components (8881 quad NAND, 8271 registers) it looks like it’s one of the boards from a PDP-11/20.
A link to a pdf with all the schematics is here, but I haven’t found a match for your board yet. Would it be possible to get a picture of the traces on the other side so we could try tracing through the logic ourselves?
http://www.bitsavers.org/pdf/dec/pdp11/1120/1120_SystemSchems_Feb70.pdf
Normally, I’d say yes, but unfortunately this board in question is at my home in Michigan. I took this photo back when I went home for Christmas :) It was supposed to be the January NTW but current events trumped the January NTW spot.
doh!
Just amazing looking back at these old systems and how low-density they were. There’s enough room on that board that even *I* could work on it!
Looks like just another discrete logic card. Those old machines didn’t have CPUs. This could be some registers or part of an ALU.
Nope, we don’t need the traces to find the match; you can just go by the way the components are laid out. Looking through the PDP-11/20 specs; the board on page 37 is the only one with a DEC 8881 in the E1 component position and four flanges on the edge connector.
The schematic description is “BUS INTERFACE and IR M725”
I’m about as familiar with the PDP-11 as I am with the bones of other Jurassic fauna ( and google won’t clarify) so I’ll have to look at the schematic a bit to puzzle out what IR stands for.
Oh, KA11 is the CPU. So IR is “Instruction Register”? My guess it’s the CPU’s interface to the bus and the storage for the instruction before it’s decoded (which looks like it’s done by M726).
Nope. Can’t be the M725. The parts list and schematic for the M725 IR/Bus interface has no 8271 registers while the picture has 9 (that I can read anyway).
I didn’t find anything in the PDP-11/20 schematics that matched, so at this point I think it’s from another similar model of PDP-11. I chose the 11/20 CPU because it’s Unibus (like the card in the picture) and a lot of the DEC ASIC’s that we can see in the pic match IC’s referenced in the schematics.
There are more PDP-11 manuals on bitsavers and I’ll try to track down this board tonight after work unless someone beats me to it.
Just to clarify: I’m saying it probably isn’t that board (unless DEC did part substitution). It very well could be the IR.
It’s almost certainly a register (8+1 bits of state in the 8271s = 1 byte /w parity) and the 8881s and 8815s are just NAND and NOR bus drivers.
I haven’t bothered to look through the support logic TTL chips yet and it’s going to be hard to do this one by dead reconing since we can’t read the chips at the top of the photo and we don’t have the other side of the PCB.
Whoooaaaa….
I remember biking through UBC one day when I was 8 and some dude was just giving these things away. I think I still have mine somewhere…
hi, i came across ur blog n i read that u’ve a sony t9. i’ve a sony t9 too, but i’ve a prob with its night mode. when i use the camera in clubs, the pics turn out real bad. like all black or all white. could u help?
As people have stated before, it is pretty safe to say the card would fit into a DEC Unibus or Qbus backplane. The upper left hand side has a few solder bridges that are probably a bus address or I/O page. I only assume the 1K resistors are for pull up. I am willing to bet the 750 ohm (violet green brown gold) resistors are bus terminators. I originally thought the S7727 DEC 8881 might be a TTL 7727 octal tristate IC, but the pin count is wrong. From the schematics Phil linked to
(note Dec parts might have non-standard locations for GND and +5 pins)
8881 = quad dual input NAND (and the pin count is correct for it too)
8815 = dual quad inverted input AND
8251 = 1 of 8 active low line selector
7460 = dual quad input AND with differental output
The 7450 looks a bit interesting. It looks to be a 2x dual dual input AND that feeds into a NOR that has an open collector differential input and look to be tri-stateable — screams bus driver. The 7460’s outputs are wire-ored to the 7450 and look like they control the gate’s connection to the backplane.
Anyway, time to do some work I that I might get paid for…
It would be really easy to figure out what this board is if you looked at the magenta handles for the part number. Unfortunately that would necessitate another picture from a different angle. Typically DEC printed the module number in white on one of the handles. The 77xx numbers on the various ICs are almost certainly date codes, meaning the board was manufactured with chips made in 1977; the xx being the week of the year, This makes it far too recent for it to be part of a pdp11/20.