PDP-11 with ATX power supply

John Wilson wilson at dbit.com
Sun Mar 8 01:43:01 CST 2015

On Sat, Mar 07, 2015 at 07:38:58PM -0800, Earl Evans wrote:
>However, unlike the DEC PSU, the ATX power supply won't supply a 60 Hz line
>time clock (LTC) signal to the backplane via BEVENT. So, my question - has
>anyone used a standard ATX PSU for a PDP-11 QBUS system, and if so, how'd
>you work around the LTC issue?

I haven't done it with an ATX PS, but years ago I set up a 4-slot
dual-height box (is that BA-11VA?) that didn't drive BEVENT L, to run
RSX11M+ which of course requires the clock, so I dangled a little piece of
perfboard in the backplane (wire-wrapped to BEVENT L and the power pins)
with a PIC CPU that generated the clock.  Code here:


... and there's an ASCII drawing of the ultra-simple circuit in a comment
block there.  If I were doing it now I'd use an 8-pin PIC.

John Wilson
D Bit

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