20 May
2019
20 May
'19
5:33 a.m.
Alright, I hooked the oscilloscope up to SRUN off of E68, and found that it
oscillates low at 58.68KHz. This oscillation is very short lived, with it
bouncing back up to high nearly instantly. Hitting the Run/Halt switch does
not have any effect on the period or amplitude of the oscillation.
On Mon, May 20, 2019 at 3:05 AM Brent Hilpert via cctalk <
cctalk at classiccmp.org> wrote:
On 2019-May-20, at 12:11 AM, Glen Slick via cctalk
wrote:
Good, that makes sense together, as the duty cycle could be expected to be
too low to light the LED driven directly.
TTL monostables weren't the most reliable components.
On Sun, May 19, 2019 at 11:48 PM Brent Hilpert
via cctalk
<cctalk at classiccmp.org> wrote:
>
> Except the SRUN (K8 SRUN L) action is not latched, so it probably
appears as
an
> active-low heartbeat pulse with some
periodicity when the processor is
in run mode.
A
low-going pulse during PH 3 every instruction cycle perhaps.
http://www.bitsavers.org/pdf/dec/pdp11/1103/1103_Schematics.pdf
Page 171 of the PDF, Lights & Switches Board schematic
The SRUN L signal (routed from the backplane through the power supply)
is fed through a 74123 retriggerable monostable multivibrator
one-shot before driving the RUN LED. If the SRUN signal is a pulsing,
the LED might effectively be driven constantly on.
I don't have the H11 schematic. It's front panel might have similar
logic driving the RUN LED.