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a few DECmate II questions

hush

Experienced Member
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Feb 7, 2022
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71
Location
MD, USA
hey all! i recently picked up my first PDP8 based machine, a DECmate II sans monitor and keyboard. i have an LK201 and i'm working on getting the parts together so i can build an adapter to a modern display using an OSSC i already have lying around from my retro gaming hobby (see here, should adapt nicely for monochrome), but i have a few questions about getting started.

it looks like this machine runs a derivative of OS/8 with WPS on top, but i've also seen mention that it can run straight OS/278. is this the case, and if so, does anyone know where to locate floppy media? i was able to find the source distribution on ftp://update.uu.se/pub/pdp8 , but no floppy images, so i'm wondering if i'm looking in the wrong place or need to build my own.

i've also seen mentioned that it is not possible to use this machine with a serial terminal- as mentioned before i'm working on building the adapter, but i'm also wondering if this is even necessary if i had a working VT lying around?

lastly, and this may seem like the silliest question of all, but i'd imagine trying to get this machine on the network in any way is a non-starter? being able to get a telnet session would be nice, but worst case scenario i could figure something out using screen(1).

thanks in advance!
 
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ftcnet

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May 4, 2019
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106
Location
BC Canada
it looks like this machine runs a derivative of OS/8 with WPS on top, but i've also seen mention that it can run straight OS/278.
That's not quite how it's done. Check out the DECmate Information & FAQ's. A DECmate II (depending on installed options) can run OS278, WPS, DOS and CPM. If your DECmate II has a hard drive, you'll probably want it to boot to Master Menu.
 

hush

Experienced Member
Joined
Feb 7, 2022
Messages
71
Location
MD, USA
That's not quite how it's done. Check out the DECmate Information & FAQ's. A DECmate II (depending on installed options) can run OS278, WPS, DOS and CPM. If your DECmate II has a hard drive, you'll probably want it to boot to Master Menu.
good info, thank you! i wasn't able to get any pictures of the internals and the seller didn't provide any details beyond that it powered on, so i'll have to wait until i have it in hand to see what it's got. my understanding is that it should be able to run OS/278 without an expansion card, and that that's only necessary for CP/M, is that correct?
 

ftcnet

Experienced Member
Joined
May 4, 2019
Messages
106
Location
BC Canada
i'm working on getting the parts together so i can build an adapter to a modern display using an OSSC
That sounds quite interesting. I'm not pleased with the state of my VR201 monitor due to the many 'cataracts' or spots, that are present. I'd like to avoid the process described to deal with monitor degredation. The VR201 screen size just seems uncomfortably cramped to use nowdays so please keep us updated on how to get an OSSC working with a VGA or HDMI display in place of a VR201 monitor.
 

hush

Experienced Member
Joined
Feb 7, 2022
Messages
71
Location
MD, USA
exactly what i was looking for, thank you so much!

That sounds quite interesting. I'm not pleased with the state of my VR201 monitor due to the many 'cataracts' or spots, that are present. I'd like to avoid the process described to deal with monitor degredation. The VR201 screen size just seems uncomfortably cramped to use nowdays so please keep us updated on how to get an OSSC working with a VGA or HDMI display in place of a VR201 monitor.
will do as soon as i have a working prototype- my gut feeling is that it should be pretty easy to get working, but you know how these things go :)
 

hush

Experienced Member
Joined
Feb 7, 2022
Messages
71
Location
MD, USA
got my DECmate today so i'm revisiting this- started making a cable for the OSSC and got stuck, so i figured i'd ask here.

i think i have the video portion down- according to this pinout, pin 12 on the BCC02 cable is mono video. i have a standard VGA cable that i've cut one end off of and stripped- green goes to pin 12 on a DB15 terminal block, black to ground. i think this is sufficient for mono video, someone please correct me if i'm wrong.

the problem i'm having is with the RJ11 bit. these instructions are a bit ambiguous:

Looking into the face of the RJ11, with the pins towards you, number the leftmost pin 1. Link as follows:
  • RJ11 pin 1 to pin 14 of the D
  • RJ11 pin 2 to +12V
  • RJ11 pin 3 to Ground
  • RJ11 pin 4 to pin 15 of the D
i'm not sure what the orientation is here. tab up? tab down? get it wrong and my DECmate gets a healthy dose of +12V as soon as i plug a keyboard in. not good. or am i overthinking this?

any thoughts?
 
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NeXT

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Oct 22, 2008
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Kamloops, BC, Canada
I'd just beep out the pins. Only one of the two innermost pins are going to have a low resistance to chassis ground so once you find the ground pin you know that +12 is right next to that.
 

hush

Experienced Member
Joined
Feb 7, 2022
Messages
71
Location
MD, USA
I'd just beep out the pins. Only one of the two innermost pins are going to have a low resistance to chassis ground so once you find the ground pin you know that +12 is right next to that.
i'll try that, thank you!

got around to inspecting the power supply today, i didn't pull it apart completely but visually speaking i think it's in good enough shape that i can rule out potential catastrophic failure- i won't be running this 24/7 anyway. tried my video adapter hack too, nothing doing, unfortunately. the system powers on, but doesn't appear to POST as i do not get anything on the screen. the OSSC also doesn't seem to recognize a signal as the LED display does not update as expected. i don't currently have the keyboard plugged in due to missing the keystone jack still, maybe it's unhappy about that and not initializing video as a result? this is my best guess right now. i've also attached a picture of the adapter i'm using:

IMG_0816.jpg

green -> mono video
black/yellow -> ground
orange -> KBD RX
grey -> KBD TX
red -> +12V

the latter four wires were added after my display testing.
 

hush

Experienced Member
Joined
Feb 7, 2022
Messages
71
Location
MD, USA
keystone jacks arrived and everything's wired up, everything beeps. plugged it in with an LK201 and my OSSC, nothing blew up but i still get no video. no LEDs on the keyboard either, like i would expect. not sure if this indicates hardware failure or (more likely) something wrong with my adapter. i'm seeing ~12V between ground and pin 7 on the DB15, as expected. mspaint picasso diagram below:

stupid.png

it looks like the VR201 might require sync-on-green, but i can't tell for sure. if that's the case then it would probably explain why i'm getting no video signal, but assuming the keyboard portion is wired up properly, shouldn't i be seeing something there? the LK201 is known-good, it works on my uVAX.
 
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