18 Jan
2015
18 Jan
'15
1:32 p.m.
On 2015-01-18 22:12, Robert Jarratt wrote:
All power pins are ok to the CPU?
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.
That will be very hard to verify without disconnecting the pins. So
let's focus on other things for the moment.
Well, I can't offer any more help on that one. Just a reflection.
Johnny
--
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
-----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 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. 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.
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 shorted
high, but I don't know. 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-description…
Johnny
Regards
Rob
--
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 -----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