On Sun, May 19, 2019 at 11:48 PM Brent Hilpert via cctalk <[email protected]> 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.
