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a few DECmate II questions

hush

Experienced Member
Joined
Feb 7, 2022
Messages
316
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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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.
 
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?
 
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.
 
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 :)
 
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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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'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.
 
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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disregard... on a whim replaced the RJ11 terminal and now it seems happy? weird...
 
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Your previous message suggests the keyboard is working, but did you get video working as well?
So, is your DM-II up and running now?
I've got one running straight WPS and have been meaning to upgrade to Master Menu and also tempted to use a floppy-emulator since RX50s are what they are.
 
Your previous message suggests the keyboard is working, but did you get video working as well?
So, is your DM-II up and running now?
I've got one running straight WPS and have been meaning to upgrade to Master Menu and also tempted to use a floppy-emulator since RX50s are what they are.
the video works, but i need to do some tweaking on the OSSC to make it actually readable- all i did was hack the end off a regular VGA cable and use an RS232 terminal block to put the wires where they needed to be. been having more trouble with the keyboard portion, the DMII complains that the keyboard is not present. i am not sure if i assembled my emulator/adapter combination incorrectly and have not had the time to try it again, nor do i have a working LK201 to test against. i am using paul koning's LK201 emulator: https://github.com/pkoning2/lk201emu
 
i'm returning to this now that i have a real LK201, and i am having the same issue as before. my adapter is simple, a DB15 terminal block from amazon and an RJ11 terminal block attached to it for the keyboard. the OSSC has VGA in so i hacked one end off a standard VGA cable. here's how i have it all wired, referencing the following pinouts:


VGA green -> DB15 pin 12 (mono out)
VGA green gnd -> DB15 pin 4 (mono gnd)
VGA gnd -> DB15 pin 5 (gnd)
RJ11 pin 1 -> DB15 pin 14 (kbd rx)
RJ11 pin 2 -> DB15 pin 6 (gnd)
RJ11 pin 3 -> DB15 pin 7 (+12v)
RJ11 pin 4 -> DB15 pin 15 (kbd tx)

i'm still getting error 16 at the display, which indicates a keyboard error. the LK201's lights pop on when the system starts so it is not dead, i do not think it is suffering from the stuck key issue as the LEDs are not stuck on, they pop on then off as expected. does my wiring look sane? if so, do i just have a sick system board? +12 is stable, i am getting -0.73v on pin 14 and and -6.8v on 15.
 
I checked my VR201. Looks like RJ11 pin 1 conencted to DB15-15 and RJ11 pin 4 connects to DB15-14.

I think the LK201 is RS-232 so -.73V isn't proper level. Likely one end is driving positive and the other negative with the miswire. Should be > +-5V.
 
I checked my VR201. Looks like RJ11 pin 1 conencted to DB15-15 and RJ11 pin 4 connects to DB15-14.

I think the LK201 is RS-232 so -.73V isn't proper level. Likely one end is driving positive and the other negative with the miswire. Should be > +-5V.
i have the biggest smile on my face right now, that did it! i got a happy beep and a welcoming DECmate II screen this time, seems like she's good to go! i had a sneaking suspicion that i had swapped the TX and RX lines, but didn't want to just switch them out for fear that something else could be wrong and doing so could exacerbate it. thank you for the assist, now i get to make myself some OS/278 floppies :)
 
so i am having a little bit of trouble getting the OS/278 image booting- i don't currently have a way to prepare 5.25" floppies, but i do have a working gotek with the flashfloppy firmware. i'm using the disks from ibiblio which should be valid RX50 disks, but i can't seem to get them into a format the gotek likes. flashfloppy claims to support RX33 and RX50 disks, but in what format? the teledisk format they are distributed in can't be read natively, and the images i get feeding them through wteledisk/td02img do not seem to be bootable.

if anyone has managed to get this working on a gotek please let me know, i was able to find this thread but it is a bit unclear what conversion needs to take place, the author of post #3 has some gotek configuration information, but using the commands they provide does not give me a bootable image, i just get the floppy disk icon on screen indicating a missing/bad disk.
 
so i am having a little bit of trouble getting the OS/278 image booting- i don't currently have a way to prepare 5.25" floppies, but i do have a working gotek with the flashfloppy firmware. i'm using the disks from ibiblio which should be valid RX50 disks, but i can't seem to get them into a format the gotek likes. flashfloppy claims to support RX33 and RX50 disks, but in what format? the teledisk format they are distributed in can't be read natively, and the images i get feeding them through wteledisk/td02img do not seem to be bootable.

if anyone has managed to get this working on a gotek please let me know, i was able to find this thread but it is a bit unclear what conversion needs to take place, the author of post #3 has some gotek configuration information, but using the commands they provide does not give me a bootable image, i just get the floppy disk icon on screen indicating a missing/bad disk.
I suspect you have to convert any floppy images to a raw sector by sector format to make it work on the DECmate II.

Could you please explain how exactly you hooked up your Gotek to the DECmate II?
Did you use a custom cable? If yes, could you please share you cable diagram.
 
I suspect you have to convert any floppy images to a raw sector by sector format to make it work on the DECmate II.

Could you please explain how exactly you hooked up your Gotek to the DECmate II?
Did you use a custom cable? If yes, could you please share you cable diagram.
the conversion's where i'm getting stuck, unfortunately, but i've been plugging away at it for a bit trying to get it working.

i'm just using the original floppy cable that came with the system for the RX50- i'm not sure if it's working properly but it should be, i don't think there's anything strange going on with the RX50 interface like some IBM drives i've used. it could be that i've gotten the conversion right but it wouldn't boot because the cable is bad, i'm really not sure. without a working system to test against i'm pretty much just guessing.
 
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