View Full Version : Fun with OS/8

January 9th, 2009, 08:04 AM

I've gotten my SBC6120 (DEC PDP/8e clone) up to booting OS/8.

It's fun learning a new old OS, and seeing where later OS's came from.

I inadvertantly learnt how to shut off the nifty command interpreter (CCL) that allows shortened commands. Non-intuitively, typing 'CCL<enter>' turns it off. Finally got it back with 'R CCL<enter>'. Whew!

I've been wondering how you 'gracefully shutdown' a PDP-8. Anyone know if you can/should do this?


January 9th, 2009, 09:57 AM
Turn the power off I guess :) Actually I don't know, I guess I should learn so I can treat my real PDP-8/e nice once it is restored.

Anyways, I guess this means that you at least got your parts for the kit? Could you perhaps treat us with a picture or two?

Lou - N2MIY
January 9th, 2009, 03:59 PM
I'm not sure that this does any good, but it seemed like a good thing to do: I always halt the processor before shutting the 8/e off. (Then I put 7605 in the SR so that restarting OS/8 will be quick next time I use the machine.)

I halt the processor first on the pdp11s also.


January 10th, 2009, 02:54 AM

(Sorry for the ignorance). How do you halt the processor? Is there a short assembly language program to do this?

(IIRC there was an undocumented 6502 instruction that put it into a one-instruction infinite loop, that was informally called HCF i.e. Halt and Catch Fire.)


Lou - N2MIY
January 10th, 2009, 04:32 AM
To halt the 8/e, I throw the halt switch on the front panel. Alternatively, op code 7402 is a halt instruction.

I highly recommend that anyone with an 8 get a copy of the "pdp8/e pdp8/m & pdp8/f small computer handbook", available here from bitsavers:


It's a huge download, but it's the bible.