20 May
2019
20 May
'19
1:05 a.m.
On 2019-May-20, at 12:11 AM, Glen Slick via cctalk wrote:
On Sun, May 19, 2019 at 11:48 PM Brent Hilpert via
cctalk
<cctalk at classiccmp.org> 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.
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.