Assembled and tested

[Bill Saltzstein]

Received mine, assembled and installed and tests out OK, THANKS!

Ready for some SIMH goodness when it comes down the pipe.

Nicely done Steve!

Bill

On Thursday, August 26, 2021 at 2:57:20 PM UTC-7 ssta...@gmail.com wrote:

Hello All!

It's been a busy summer, but I'm happy to report that the first batch of I/O Expanders for the PiDP-11 are ready to ship! I've put together a kit on Tindie that contains everything needed to expand your PiDP-11 with 16 GPIO pins (up to a maximum of 128). I have also documented the installation instructions on Hackaday.

At the moment, WiringPi is probably your best bet to interface with the I/O Expander using the MCP23016 extension. I'll be working on a more targeted library in the coming days and will also be working on adding a new device to SimH that will allow programming GPIO pins from the front panel in the next few days.

Due to the global supply shortage some of the tooling needed to create the kits ended up being a little more expensive than originally quoted. As a result, I had to raise the price to 29 USD over the original 25 USD to cover the increased cost. I'm not happy about the price change, so as a compromise, I created a discount code for folks on the mailing list that would be interested in ordering before Labor Day at the original 25 USD price.

If you're still interested, you can purchase kits from Tindie using the discount code 1A5816D3 at: https://www.tindie.com/products/sstallion/pidp-11-io-expander-kit/

Instructions and other project information can be found on Hackaday at: https://hackaday.io/project/181311-pidp-11-io-expander

Lastly I'd like to send a heartfelt "Thank You" to Oscar and everyone on the list for being so supportive of the project. I truly hope this can add a little extra fun to your PiDP-11 hacking!

Cheers,

Steve

[Steven Stallion]

That's great to hear! I've run into a minor delay on account of WiringPi being deprecated. I'm putting the finishing touches on a userspace I2C library for Linux that I'll submit upstream once the dust clears. Once that is finished, I should be able to put together a reference device in SimH very quickly using that library and libgpiod.

Thanks again!

Steve

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[Heinz-Bernd Eggenstein]

Sounds great, some sort of hook inside simh to communicate over I2C would be great.

Which makes me wonder...do you care about the P(i)DP-8 as well? I understand the "real" PDP-8 came with an A/D-converter, something that would be great to have in the simulated one as well and with an I2C bridge that should be doable perhaps? -(I wasn't sure whether you are following the PiDP-8 list as well where this dicussion should eventually end up I guess).

Cheers

HBE

[Bill Saltzstein]

Love the PDP-8 idea.  There were both analog and digital I/O peripheral cards if I recall.  

I’ll have to search for the PiDP-8 group; I wasn’t aware of it.

Take care,

Bill

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[Johnny Billquist]

The PDP-8 didn't come with an A/D converter anymore than a PDP-11 did.
They were available to add, if you bought them, for both machines.

Johnny

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Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol

[Heinz-Bernd Eggenstein]

I was probably fooled by the marketing brochure http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp8/pdp8/PDP-8_Brochure_Nov64.pdf which mentions "Basic 18k$ configuration includes [..] wired-in A/D-converter" but if you read that section closely, I guess it means that is was just prepared for it... oh well. Anyway, the newest OS/8 version that the tangentsoft distribution for the PiDP-8 offers has a BASIC that has ADC readout as a user defined function  https://github.com/tangentsoft/pidp8i/blob/f4eb38bdc81c519bb03eeea394dd33ad6faf4f28/src/os8/ock/LANGUAGE/BASIC/UF.PA  (and a similar API  for FORTRAN ) so if SIMH could be nmade to support it, the ADC would be very easy to use from the OS/8 user perspective .... analog game controllers with the help of a Raspberry Pi Pico µC perhaps??

Cheers

HB

[Steven Stallion]

Putting together an ADC/DAC expansion over I2C wouldn't be tough at all. Out of curiosity, what sort of capabilities are you looking for? I don't have a PiDP-8 myself, but I took a quick look at the schematic and it doesn't seem that the I2C pins were brought out on that board like they were on the PiDP-11 - can anyone confirm this is the case?

Cheers,

Steve

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[Heinz-Bernd Eggenstein]

I just got my PiDP-8 and I can confirm that at least the current version does indeed have  an unpopulated pad next to the PI connector intended for an angled connector to be soldered in. It definitely connects 3.3V, SDA and SCL, I'm not sure whether the 4th pin is for GND or a free GPIO used for interrupts perhaps (as with the PiDP-11).

I was wondering about using the Raspberry Pi Pico as an off-the-shelf extender for this, it does support running as an I2C *slave* in principle (unfortunately the Micropython support for I2C *slave* mode seems to be lacking (??), but there is always the C SDK ) and the Pico has 3 pins that can be used as input for the 12 bit ADC ... (actually it has four ADC channels but one is hard-wired to the die-temperature sensor, AFAIK). This config would be super-inexpensive and plug-and-play. Needless to say the Pico's ADC doesn't support the voltage range of the original PDP-8's ADC equipment but who cares.  I guess the idea whould be that SIMH would just pass information to the Pico which would then implement all the necessary logic and real-time action and would report results and status changes back to SIMH on the PI. 

Anyway, what I would be looking for (at a minimum) is to be able to query the current digital readout using the respective IOT instructions (which would probably then work as well from BASIC or Focal or FORTRAN, see link above), from at least (say) two multiplexed channels, with 10 bit resolution. Then I would already be super-happy :-).
Bonus would be to support the entire set (a handful or so) of low level ADC-related instructions, which I think allowed advanced things like to set up the interface to sample a given channel at a given frequency and fill an "array" in memory with those values. But let's not get carried away :-) 

I guess the experts here would know which of (I think) many ADC options that you could use with the PDP-8 would be easiest to simulate for starters.

Thoughts?

Cheers

HB

[Steven Stallion]

Thanks! Sure, you could do everything with an MCU but there will be a fair amount of firmware you'll need to write to provide a good register interface to the Raspberry Pi. If you're looking to do a one-off, this could be a good way to go! If you're wanting to mass produce something, there are ICs designed to handle this exact use case and since the requirements aren't very high, you could get away with something fairly small. For example, a single-ended 12-bit I2C ADC starts around 1$ and goes up from there depending on footprint, number of channels, etc.

Cheers,

Steve

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