Next project: 11/24. Does it need memory?--Working-ish!

Chris Zach cz at
Sun Oct 25 20:01:10 CDT 2020

Ok, so now the three old style 11/24 CPU boards seem to be working. Ish. 
The problem with the processor boards turned out to be the switches: On 
my original 11/24 board it would work only at 19200. This is because the 
switch pack is dirty and the contacts ain't working.

Solution: Spray 95% isopropyl alcohol right into the switch housing from 
the top with all switches set to off. Then toggle the switches, then 
toggle again, spray again, and set them. Board 1 now works at 9600 baud.

Board 3 was a bit more odd: It didn't do anything at any baud. So I set 
both switch packs to all off, then did the above cleaning, then set them 
properly and sure enough it comes up into ODT at 9600 baud.

The last board is a new style 11/24 and it doesn't do anything but it 
does have three switch packs. So I just need to find the manual for it, 
set the switches, and give it a try.

In the meantime the UNIBUS problem also appears to be fixed: The problem 
was that sure enough: One of the memory slot SPC's (4) did not have the 
DMA jumper. Found it pretty quickly with a continuity meter and checking 
slot C pins 1,3 (top) for continuity. On the good side slot 9 does have 
a DMA jumper, so I simply put the RX02 controller in slot 4, put the 
G727 in slot 7, then put the TS11 controller (hex) in slot 8, then a 
knucklebuster in slot 9 along with the 9302 terminator and all works great.

Isn't UNIBUS simple! Sorry, Q-Bus doesn't need a terminator, doesn't 
have weird DMA stuff, and if you really need to put a card on a 
particular side you can always grab a DLV11 (everyone has these) and use 
it as a spacer. Anyone even know why Q-Bus doesn't need termination; 
they used to do it with say the BDV11 but they just stopped doing it 
after awhile.

Next step is to put the 11/24 away for the week and order a good 10 feet 
of 40 pin ribbon cable so I can make an extension cable for the RX02. 
Then I should be able to plug that in, set the RX02 to RX02 mode on the 
drive (it's hooked to the 11/93's RXV11 now), key in a bootstrap from 
the console, and see if I can boot an RX02 RT11 floppy.

Question: Can an RX02 boot an RX01 floppy formatted single density with 
the DY: driver? Can it read an RX02 floppy in one drive and an RX01 
floppy in the other or do you have to set the switches and use the right 
controller card (that would be stupid, but sooooo DEC!)

Thanks everyone here and on the Discord for the help Getting there bit 
by bit.

On 10/23/2020 8:07 PM, Chris Zach via cctalk wrote:
> And "in the meantime" I figured something was wrong on the Unibus, so I 
> pulled all of the cards except CPU, memory, and the 9302 terminator.
> Still flunks in any memory references in ODT. Weird.
> Then I pulled the memory card so it was just the CPU. Same thing.
> Then I figured might as well put the memory back, and pull the 
> terminator. Sure enough, memory board LED goes red....
> But the CPU can now read and write to memory locations via ODT. Loading 
> 100 into location 0 works, and I can read location 0 and now see 100.
> That's weird. It looks like the problem is using a 9302 terminator 
> instead of a 9312. Is there differences between the 930, 9302, 9312, and 
> other terminators by chance (yes, it's in the last slot in the AB slot).
> Weird. But getting closer every day...
> C

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