18 Jan
2015
18 Jan
'15
1:47 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Johnny
Billquist
Sent: 18 January 2015 21:33
To: cctalk at classiccmp.org
Subject: Re: VT101 8085 CPU Fault
On 2015-01-18 22:12, Robert Jarratt wrote:
pins on the working one. It looked like the voltage might be spiking upwards,
but it is hard to tell because I don't have a working logic analyser.
All power pins are ok to the CPU?
I checked Vcc and Vss and they appeared to be fine (5V and 0V respectively).
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of
Johnny Billquist
Sent: 18 January 2015 20:49
To: cctalk at classiccmp.org
Subject: Re: VT101 8085 CPU Fault
On 2015-01-18 21:37, Robert Jarratt wrote:
Yes there is, but it looks odd, and very different to when I checked the address No stuck, high.
Is there any activity on any of the address pins? If those also are
dead, either the whole CPU is dead, or else it is disabled by something.
I wouldn't care much for a logic analyzer at this
point. A good scope will tell
you more. Nice sharp edges to signals when they shift. Times that look
reasonable... Steady levels, and correct levels.
It will never be steady with a scope because the address lines won't be a regular
waveform. That said they looked very different on the faulty board to how they looked on
the good board.
If those
are showing activity then the RD pin is either dead, or
shorted somewhere, I'd guess.
RD and WR are active low, and they are both high, so I suppose they could be I hope
you are checking the right pins... :-)
Me too, although I have checked multiple times. I am using this page
to give me the pinout:
http://scanftree.com/microprocessor/Pin-Diagram-of-8085-and-Pin-descri
ption-of-8085
Johnny
Regards
Rob
> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of
> Bob Rosenbloom
> Sent: 18 January 2015 20:11
> To: General at classiccmp.org; Discussion at classiccmp.org:On-Topic and
> Off- Topic Posts
> Subject: Re: VT101 8085 CPU Fault
>
> On 1/18/2015 12:07 PM, Robert Jarratt wrote:
>> 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
>>>
>>>> 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
>> CPU
>>> being held reset all the time?
>>>
>>> -tony
>>> =
>>
>
>
> --
> Dentopedalogy is the science of opening your mouth and putting your
> foot
in it.
> I've been practising it for years.
> -Prince Philip
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol