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PDP-8 Single Board using IM6100

O

oldmicros

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Nov 13, 2015
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Location
Missouri
The Holiday break has given me some quality time to spend on a single board computer using the IM6100 (actually Harris 6100.)

Got the PCBs earlier this month and was finally able to get one assembled.
Control Panel is nothing but switches and LEDs but for me was the most difficult part.

IMG_0824.jpg IMG_0826.jpg

I plan to post all design details on Github once I am further along.
Also have extra boards and parts (including switches and LEDs) if anyone would be interested in the future.

At this point it is passing the processor and extended memory maindecs.

The serial port on the SBC serves a dual function as the KL8E compatible port and also as a debug port.
It is very useful as a debug port since I can trace program execution and print the bus contents for every memory cycle (R/W/IOT)

The SD card is FAT32 and contains disk images which may be assigned to either drive of a dual RX01.
I am currently working with the RX8E maindec.
My plan was to NOT implement the deleted data function.
Does anyone know if this bit is actually used anywhere (besides the maindec)?

-Bill
 
Thanks. I used Kicad to design the PCB.

I originally prototyped this using wirewrap and (many) TTL ICs but had some CPLDs laying around.
Makes PCB layout and changing the logic a much easier task.
 
I've never run across anything using the deleted data function. The RX floppy images around are just the sector contents.
 
Excellent! Do you perhaps have any plans to make a few assembled units available to folks like me who are unable to assemble one on my own?

smp
 
djg said:
I've never run across anything using the deleted data function. The RX floppy images around are just the sector contents.
Click to expand...

Thanks for the response.
I agree. It hasn’t been included in any of the image files I’ve seen.
It’s somewhat of a pain to implement so I don’t think I will.
 
smp said:
Excellent! Do you perhaps have any plans to make a few assembled units available to folks like me who are unable to assemble one on my own?

smp
Click to expand...

Absolutely.
I would even be willing to donate one to someone who is more familiar with the operation of a “real” PDP-8.
Just to get some more knowledgeable input on the design.
 
OK! Great to hear.

Please be sure to post your progress, and also post when you feel you're ready to sell a set.

smp
 
I have some of these chips lying around. I built Robert Armstrong's 6120's and he actually had a 6100 design done in the much the same vein as the 6120. It used GAL's, and he apparently decided not to release it because of the 4K limitations and the relative rarity/slowness (at 5V) of the chips.

So is this FPGA based or does it use a real IM6100? Not sure due to picture resolution.

I've always thought that the functions of the 6102 (to get to 32K, among other things)could be duplicated (and hopefully improved) by an FPGA. Supposedly the 6100 and 6102 were basically custom masked gate arrays.
 
Last edited:
Slob said:
So is this FPGA based or does it use a real IM6100?
Click to expand...

It uses a real 6100 currently running at ~4Mhz.
It has a PIC on the DX bus to handle the IOTs and Control Panel memory.
The PIC also has the serial port and SD Card interface.
One of the CPLDs is general TTL control logic and the other CPLD is nothing but muxes and latches for the Front Panel.

The PIC is nice because it can handle the IOTs coming from the processor.
So far I have implemented the extended memory, serial port, and RX disk IOTs.
I have also defined custom IOTs for writing to the panel display, selecting SD card files for disk images, and various other functions.

Some of this has yet to be tested - taking it step by step.
My next step after getting through the RX8E maindec is to try to boot OS/8.

-Bill
 
IM6100 single board computer update -I have got through the RX8E maindec and OS/8 will boot.

Video here - https://youtu.be/y52wcy1FXfs

It would be nice to be able to access larger disk images.
I guess this would require a custom handler for OS/8?

-Bill
 
Great progress. I found a tube and a half of these. Wow, have they become expensive, and 6120's, nearly unobtainable. I hope that you make boards available; I can program PIC's, but CLPD's, probably not.

I'm surprised that the speed looks usable. I had read that these were dogs compared to the 6120 and real PDP8/E. Apparently, it takes 10V to get it close to that speed "overclocked", and the voltage translation hardware to interface that to a +5 volt support chip set would be daunting.
 
kb811 said:
6120: I got some from utsource.net ..
Look how many they have in stock!
Click to expand...

I don't believe their 'stock' numbers. It looks like just about any part has either ~23000 or ~29000 in stock. Highly doubtful if those are accurate numbers.
 
oldmicros said:
IM6100 single board computer update -I have got through the RX8E maindec and OS/8 will boot.

Video here - https://youtu.be/y52wcy1FXfs

It would be nice to be able to access larger disk images.
I guess this would require a custom handler for OS/8?

-Bill
Click to expand...

Great design, thanks for using through-hole rather than surface mount components which should make it much easier to assemble. And is that a D830? I still have one of those somewhere, great workhorse machines with a built in serial port.
 
oldmicros said:
It would be nice to be able to access larger disk images.
I guess this would require a custom handler for OS/8?
Click to expand...
OS/8 file systems can support at most 1 million words (4096 blocks of 256 words=1048576 words or 1572864 bytes). This is why larger devices present as multiple units. For this reason I would suggest that you emulate the RK05 which would allow you to mount the simh disk images. This is pretty much what everyone does because it means you don't need a custom handler. The RK05 controller is a Data Break device and I have no idea if your approach with the PIC allows the pic to directly talk to the 6100's memory.

What a fun project!
 
bifo86 said:
Great design, thanks for using through-hole rather than surface mount components which should make it much easier to assemble. And is that a D830? I still have one of those somewhere, great workhorse machines with a built in serial port.
Click to expand...

Thank you. I also much prefer though-hole assembly. The laptop is a D630 - it has been going strong for years now and is my go to machine because of the "real" serial port.
 
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