11 Oct
2002
11 Oct
'02
12:37 p.m.
Okay, it is a PDP-8/L, but I don't remember an -8/L with the kind
of paddle switches this one has... I seem to remember them being
the rocker kind like on a pdp-8/I
Megan
11 Oct
11 Oct
2:06 p.m.
New subject: PDP-8/L troubleshooting (was Re: New acquisition, and question)
--- Megan <mbg(a)theworld.com> wrote:
Okay, it is a PDP-8/L, but I don't remember an
-8/L with the kind
of paddle switches this one has... I seem to remember them being
the rocker kind like on a pdp-8/I
All of my -8/Ls (3.5) have PDP-8/e-style toggle switches. My -8/I does
have the rocker switches you describe.
The 1970 Small Computer Handbook shows -8/Ls with paddle switches.
Still a nice find, though. My -8/L is currenly my showcase machine -
I fire up the ASR-33 and the PC04 (PC05?) and load FOCAL for folks.
It was also my first-ever -8 - Dayton Hamfest, 1982, $35 + 8" floppy
drive in trade.
Got some minor processor glitch I haven't tracked down yet... I get the
FOCAL prompt, but it won't load Hammurabi from either the ASR-33 or
the high-speed reader. Most of the basic functionality is there - it
runs an inchworm just fine. Once I fix the problem, I'll reattach
the BM08 and bring it back up to 12KW and show people paper-tape BASIC
and Star Trek (after I fix the tear in my floating-point tape ;-)
When you get to debugging it and if you see any behavior that leads you
to think there are hardware problems, after cleaning the card fingers,
take a hard look at any 7474 chips. I rigged up a test clip to an
automated IC tester to debug M-series modules out of the circuit (having
never written any software to drive my VIC-20 M-series tester) and
found that the most common chip to die anywhere in the machine was
the 7474 dual D flip-flop. Unfortunately, there are several of them
in the M220 Major Registers modules and this simplistic tester isn't
able to cleanly test them because of the multiple interconnects. I
have a small box of "to-be-repaired" M-series modules from my -8/L
collection. It's mostly M220s and M216s, with an occasional M160 and
M111.
-ethan
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8:16 p.m.
New subject: PDP-8/L troubleshooting (was Re: New acquisition, and question)
On the FOCAL issue, I think I read that FOCAL can't
load text very quickly - you have to stop and start
the tape every line or two. I have noticed this with
my PDP/8e clone and not-very-fast (around 100 CPS)
paper tape reader. It may use its own intepreter to
store coding in RAM, so it might be very slow in this
area. If you can load FOCAL itself in via paper tape,
this kind of proves that the PTR itself is OK.
--- Ethan Dicks <erd_6502(a)yahoo.com> wrote:
--- Megan <mbg(a)theworld.com> wrote:
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Okay, it is a PDP-8/L, but I don't remember
an
-8/L with the kind
of paddle switches this one has... I seem to
remember them being
the rocker kind like on a pdp-8/I
All of my -8/Ls (3.5) have PDP-8/e-style toggle
switches. My -8/I does
have the rocker switches you describe.
The 1970 Small Computer Handbook shows -8/Ls with
paddle switches.
Still a nice find, though. My -8/L is currenly my
showcase machine -
I fire up the ASR-33 and the PC04 (PC05?) and load
FOCAL for folks.
It was also my first-ever -8 - Dayton Hamfest, 1982,
$35 + 8" floppy
drive in trade.
Got some minor processor glitch I haven't tracked
down yet... I get the
FOCAL prompt, but it won't load Hammurabi from
either the ASR-33 or
the high-speed reader. Most of the basic
functionality is there - it
runs an inchworm just fine. Once I fix the problem,
I'll reattach
the BM08 and bring it back up to 12KW and show
people paper-tape BASIC
and Star Trek (after I fix the tear in my
floating-point tape ;-)
When you get to debugging it and if you see any
behavior that leads you
to think there are hardware problems, after cleaning
the card fingers,
take a hard look at any 7474 chips. I rigged up a
test clip to an
automated IC tester to debug M-series modules out of
the circuit (having
never written any software to drive my VIC-20
M-series tester) and
found that the most common chip to die anywhere in
the machine was
the 7474 dual D flip-flop. Unfortunately, there are
several of them
in the M220 Major Registers modules and this
simplistic tester isn't
able to cleanly test them because of the multiple
interconnects. I
have a small box of "to-be-repaired" M-series
modules from my -8/L
collection. It's mostly M220s and M216s, with an
occasional M160 and
M111.
-ethan
__________________________________________________
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13 Oct
13 Oct
9:08 a.m.
New subject: PDP-8/L troubleshooting (was Re: New acquisition, and question)
--- Loboyko Steve <sloboyko(a)yahoo.com> wrote:
On the FOCAL issue, I think I read that FOCAL
can't
load text very quickly - you have to stop and start
the tape every line or two.
An ASR-33 for DEC hardware has a "reader run" relay and
current loop. The CPU steps the reader one character at
a time to prevent this sort of thing. My ASR-33 _is_
one of these.
I have noticed this with
my PDP/8e clone and not-very-fast (around 100 CPS)
paper tape reader. It may use its own intepreter to
store coding in RAM, so it might be very slow in this
area.
The DEC highspeed reader controls the tape feed, just like
a TTY. This sort of thing was a problem in the old days, so
DEC engineered solutions for it.
If you can load FOCAL itself in via paper tape,
this kind of proves that the PTR itself is OK.
The PTR itself is OK. Where I suspect the problem is in the CPU.
The BIN loader (which loads FOCAL) does not use a wide range of
instructions. I expect that I have a dirty card edge or blown gate
that is causing less-common instructions to fail in interesting
ways. I need to sit down with the diag tapes (which I have) and
the instructions (which I also have) and run this box through its
paces, one paper tape at a time.
--- Ethan Dicks <erd_6502(a)yahoo.com> wrote:
> Got some minor processor glitch I haven't tracked
> down yet... I get the FOCAL prompt, but it won't load
> Hammurabi...
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