19 Jan
2015
19 Jan
'15
11:37 a.m.
Using a scope, look at the address lines and/or data lines at power
up, just after system reset.
The pulses will probably vary in width but should all be the same amplitude.
If you see something like stair stepping: where a pulse starts out at
5 volts and drops, for example to 3 volts and then drops to 0 volts,
then you might have two devices trying to access the same line at the
same time.
Devices on the same line may include a ram, rom, I/O ports, etc.
This could cause the processor to "hang up" and act erratic.
A schematic of the board would be helpfull if you have one.
Sandy
On 1/18/15, Bob Rosenbloom <bobalan at sbcglobal.net> wrote:
On 1/18/2015 12:07 PM, Robert Jarratt wrote:
--
Dentopedalogy is the science of opening your mouth and putting your foot in
it.
I've been practising it for years.
-Prince Philip
No, I checked that and it isn't. It is an
active low signal and it is
high.
Regards
Rob
What about the READY pin? Stuck low?
Bob
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
Sent: 18 January 2015 19:16
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: VT101 8085 CPU Fault
CPU
The terminal controller board on my VT101 is not
working, if it
displays anything it is random characters. I have used my scope to
check the 8085 CPU. It has power, it is outputting a valid clock, but
there is no activity on the RD,WR and ALE pins. I am guessing the 8085
is bad, but before I go replacing it I wanted to check if anyone knew
of anything else that might cause the 8085 to misbehave (ie am I seeing
symptoms
or a cause?).
What is the state of the reset input to the 8085? In other words, is the being held reset all the time?
-tony
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