Next project: 11/24. Does it need memory?

Noel Chiappa jnc at
Tue Oct 20 12:47:57 CDT 2020

    > From: Chris Zach

    > Unibus can get annoyed at a lot of things .. Q-Bus is much simpler

Not sure I'd concur with that latter. In analog terms the UNIBUS and QBUS are
almost identical (which is why the same driver chips such as 8641's are used
with both), and at the digital level they essentially identical (asynchronous
interlocked request/response for read and write; interrupts using
daisy-chained grant lines, with transmitted vectors; DMA, using the basic
read/write protocol to transfer data). The (not very) big differences are that
the QBUS multiplexes address and data onto a single set of lines, and the more
complex multi-level interrupt using a shared single grant line; in both, more
complex than the UNIBUS.

Perhaps you meant 'easier to use', and that may be so, since most QBUS
systems are much smaller (physically).

    > If I could disable them I could do a normal DL11 and see what I see

Looking at the docs, I don't see any way to disable the on-board serial
lines. You could probably cut etches to disable them, but I would advise
against that, because there are easier/better ways to go.

It should be quite easy to investigatwe where the problem is: look at the
'read receive 1 CSR' line, on pin 15 of E106 (with the 'halt' switch on). If
that's not hopping around, the CPU isn't running. So then we'd need to look
at the basic clock, and see if that's running; if so, then the CPU chip may
be failed; we'd need to look at the PAX lines to confirm that. If that CSR
line is active, there's a fault somewhere in the console serial line
hardware; first step would be to feed characters into the machine, and see if
they're coming out the UART.

If you don't want to mess with all that, there are CPU boards on eBait for
not too much money. (I'd be interested in buying the non-working CPU board,
if you go that way.)


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