VT101 8085 CPU Fault

[Robert Jarratt]

> -----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:
> > 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.
> 

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.


> 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-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