19 May
2019
19 May
'19
11:05 p.m.
This is a continuation of my post from about a week and a half ago. The
weekend I had some free time, so I returned, armed with a oscilloscope and
logic analyzer, to try and figure out what is wrong with my H11A. At first,
I tried to use the logic analyzer to confirm that the four clock signals on
the MCP-1600 chipset were working properly. After a day of confusing and
mixed up signals (I don't really use this type of equipment very often), I
realized that my logic analyzer was picking up the signals incorrectly. I
switched over to the oscilloscope and was able to see that the very basics
of the CPU were working. After that, I decided to try and find out why the
Run/Halt light was not coming on when I hit the switch. Looking at the H11
schematics, the light relies on the SRUN signal coming off of the
backplane. The problem I am currently facing is I cannot find where the CPU
board generates the SRUN signal. If anyone who is more experienced that me
knows how the M7264 generates the SRUN signal, that would be wonderful.
Thank You, Gavin
20 May
20 May
12:09 a.m.
On Sun, May 19, 2019 at 8:05 PM Mister PDP via cctalk
<cctalk at classiccmp.org> wrote:
After that, I decided to try and find out why the
Run/Halt light was not coming on when I hit the switch. Looking at the H11
schematics, the light relies on the SRUN signal coming off of the
backplane. The problem I am currently facing is I cannot find where the CPU
board generates the SRUN signal. If anyone who is more experienced that me
knows how the M7264 generates the SRUN signal, that would be wonderful.
http://www.bitsavers.org/pdf/dec/pdp11/1103/1103_Schematics.pdf
Page 27 of the PDF, LSI-11 CPU MODULE (K8) schematic
Grid position B1, the SRUN L signal is driven on to the backplane bus line AF1.
I have no idea how the logic works on the M7264 module that drives that signal.
2:48 a.m.
On 2019-May-19, at 9:09 PM, Glen Slick via cctalk wrote:
On Sun, May 19, 2019 at 8:05 PM Mister PDP via cctalk
<cctalk at classiccmp.org> wrote:
It looks like the CPU chipset is putting a binary 'state action code' onto the
WMIB 18-21 lines (sources on page K2) during clock phase 3 (PH 3 H at gate E45.10).
The action code is decoded to 1 of 8 actions by E68.
Most of the states are latched by the subsequent flip-flops,
and those states are cleared or set by the action codes.
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.
After that, I decided to try and find out why the
Run/Halt light was not coming on when I hit the switch. Looking at the H11
schematics, the light relies on the SRUN signal coming off of the
backplane. The problem I am currently facing is I cannot find where the CPU
board generates the SRUN signal. If anyone who is more experienced that me
knows how the M7264 generates the SRUN signal, that would be wonderful.
http://www.bitsavers.org/pdf/dec/pdp11/1103/1103_Schematics.pdf
Page 27 of the PDF, LSI-11 CPU MODULE (K8) schematic
Grid position B1, the SRUN L signal is driven on to the backplane bus line AF1.
I have no idea how the logic works on the M7264 module that drives that signal.
3:11 a.m.
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.
4:05 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.
8:33 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.
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bhilpert＠shaw.ca -
glen.slick＠gmail.com -
vintagecomputersmn＠gmail.com