8 Oct
2023
8 Oct
'23
8:34 a.m.
-----Original Message-----
From: wrcooke(a)wrcooke.net <wrcooke(a)wrcooke.net>
Sent: 08 October 2023 04:15
To: rob(a)jarratt.me.uk; Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
Subject: Re: [cctalk] VT100: Failing 2114 Chip Replaced With One With The
Same Fault
Many thanks for the suggestion. This hadn't crossed my mind, so I checked. All the
things that I could identify on the schematic that connect to the bus (UART, interrupt
vector, flag buffer and modem signals) seem not to be enabled. I have looked at what is
sinking the data bus, there is a buffer which seems to be OK and the 8251 PIC. The PIC is
harder to check but I can see it is not selected and the input pins don’t appear to be
shorted.
Not really sure what else to consider.
On 10/07/2023 5:35 PM CDT Rob Jarratt via cctalk
<cctalk(a)classiccmp.org>
wrote:
I find this really hard to explain. It can't be the chip selection
logic because then the addresses 0x2400-0x2407 would also fail and I
checked the CS signal with the logic analyser just to be sure. I also
checked the address lines directly on the RAM chip for any stuck bits
and they seemed fine too.
What are the chances of two 2114 chips failing at exactly the same address?
Is there some failure mode I might not be considering?
Rob
Perhaps it isn't the 2114 or its associated circuit at all. Maybe some other
device is being incorrectly selected by that address and driving (half) the bus
low? Just a thought.
Will
If you want to build a ship, don't drum up people to collect wood and don't
assign them tasks and work, but rather teach them to long for the endless
immensity of the sea.
Antoine de Saint-Exupery
8 Oct
8 Oct
11:35 a.m.
New subject: VT100: Failing 2114 Chip Replaced With One With The Same Fault
Do you have one of those eprom programmers which also do device checks ?
They might do a check of the supposed faulty ram out of circuit. If you
don't have one you could probably write one for any convenient device you
have to hand such as an arduino. Exercising the ram with port writes will
be painfully slow compared with a normal ram test but with only 2K to test
it shouldn't take too long.
On Sun, Oct 8, 2023 at 9:35 AM Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
wrote:
other
-----Original Message-----
From: wrcooke(a)wrcooke.net <wrcooke(a)wrcooke.net>
Sent: 08 October 2023 04:15
To: rob(a)jarratt.me.uk; Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
Subject: Re: [cctalk] VT100: Failing 2114 Chip Replaced With One With The
Same Fault
> On 10/07/2023 5:35 PM CDT Rob Jarratt via cctalk <
cctalk(a)classiccmp.org>
wrote:
>
>
> I find this really hard to explain. It can't be the chip selection
> logic because then the addresses 0x2400-0x2407 would also fail and I
> checked the CS signal with the logic analyser just to be sure. I also
> checked the address lines directly on the RAM chip for any stuck bits
> and they seemed fine too.
>
>
>
> What are the chances of two 2114 chips failing at exactly the same
address?
Is there
some failure mode I might not be considering?
Rob
Perhaps it isn't the 2114 or its associated circuit at all. Maybe some
device is being incorrectly selected by that
address and driving (half)
the bus
low? Just a thought.
Many thanks for the suggestion. This hadn't crossed my mind, so I checked.
All the things that I could identify on the schematic that connect to the
bus (UART, interrupt vector, flag buffer and modem signals) seem not to be
enabled. I have looked at what is sinking the data bus, there is a buffer
which seems to be OK and the 8251 PIC. The PIC is harder to check but I can
see it is not selected and the input pins don’t appear to be shorted.
Not really sure what else to consider.
Will
If you want to build a ship, don't drum up people to collect wood and
don't
assign them tasks and work, but rather teach them
to long for the endless
immensity of the sea.
Antoine de Saint-Exupery
11:37 a.m.
New subject: VT100: Failing 2114 Chip Replaced With One With The Same Fault
Another possible approach is to trigger the logic analyser on a write
access to that ram address, preferably with the probes on the ram itself.
Look at the resulting captures .. does it seem consistent with the code
and other accesses ?
On Sun, Oct 8, 2023 at 12:35 PM Adrian Godwin <artgodwin(a)gmail.com> wrote:
Do you have one of those eprom programmers which also
do device checks ?
They might do a check of the supposed faulty ram out of circuit. If you
don't have one you could probably write one for any convenient device you
have to hand such as an arduino. Exercising the ram with port writes will
be painfully slow compared with a normal ram test but with only 2K to test
it shouldn't take too long.
On Sun, Oct 8, 2023 at 9:35 AM Rob Jarratt via cctalk <
cctalk(a)classiccmp.org> wrote:
>
>
> > -----Original Message-----
> > From: wrcooke(a)wrcooke.net <wrcooke(a)wrcooke.net>
> > Sent: 08 October 2023 04:15
> > To: rob(a)jarratt.me.uk; Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
> > Subject: Re: [cctalk] VT100: Failing 2114 Chip Replaced With One With
> The
> > Same Fault
> >
> >
> >
> > > On 10/07/2023 5:35 PM CDT Rob Jarratt via cctalk <
> cctalk(a)classiccmp.org>
> > wrote:
> > >
> > >
> > > I find this really hard to explain. It can't be the chip selection
> > > logic because then the addresses 0x2400-0x2407 would also fail and I
> > > checked the CS signal with the logic analyser just to be sure. I also
> > > checked the address lines directly on the RAM chip for any stuck bits
> > > and they seemed fine too.
> > >
> > >
> > >
> > > What are the chances of two 2114 chips failing at exactly the same
> address?
> > > Is there some failure mode I might not be considering?
> > >
> > > Rob
> >
> > Perhaps it isn't the 2114 or its associated circuit at all. Maybe some
> other
> > device is being incorrectly selected by that address and driving (half)
> the bus
> > low? Just a thought.
>
> Many thanks for the suggestion. This hadn't crossed my mind, so I
> checked. All the things that I could identify on the schematic that connect
> to the bus (UART, interrupt vector, flag buffer and modem signals) seem not
> to be enabled. I have looked at what is sinking the data bus, there is a
> buffer which seems to be OK and the 8251 PIC. The PIC is harder to check
> but I can see it is not selected and the input pins don’t appear to be
> shorted.
>
> Not really sure what else to consider.
>
> >
> > Will
> >
> > If you want to build a ship, don't drum up people to collect wood and
> don't
> > assign them tasks and work, but rather teach them to long for the
> endless
> > immensity of the sea.
> >
> > Antoine de Saint-Exupery
>
>
1:13 p.m.
New subject: VT100: Failing 2114 Chip Replaced With One With The Same Fault
Thanks Adrian,
I am not sure if the eprom programmer I have will do what you suggest, I don’t have an
Arduino but I do have a Raspberry Pi that I could probably employ in testing the RAM. I
may look into that.
I will look again at the writes. I have seen that the test pattern (0xAA) is written
consistently to many other locations, including some to the seemingly faulty chip, so it
is hard to think how the wrong data may be getting written, but I think I can check this
fairly easily just to be sure.
Regards
Rob
From: Adrian Godwin <artgodwin(a)gmail.com>
Sent: 08 October 2023 12:38
To: rob(a)jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Subject: Re: [cctalk] Re: VT100: Failing 2114 Chip Replaced With One With The Same Fault
Another possible approach is to trigger the logic analyser on a write access to that ram
address, preferably with the probes on the ram itself. Look at the resulting captures ..
does it seem consistent with the code and other accesses ?
On Sun, Oct 8, 2023 at 12:35 PM Adrian Godwin <artgodwin(a)gmail.com
<mailto:artgodwin@gmail.com> > wrote:
Do you have one of those eprom programmers which also do device checks ? They might do a
check of the supposed faulty ram out of circuit. If you don't have one you could
probably write one for any convenient device you have to hand such as an arduino.
Exercising the ram with port writes will be painfully slow compared with a normal ram test
but with only 2K to test it shouldn't take too long.
On Sun, Oct 8, 2023 at 9:35 AM Rob Jarratt via cctalk <cctalk(a)classiccmp.org
<mailto:cctalk@classiccmp.org> > wrote:
-----Original Message-----
From: wrcooke(a)wrcooke.net <mailto:wrcooke@wrcooke.net> <wrcooke(a)wrcooke.net
<mailto:wrcooke@wrcooke.net> >
Sent: 08 October 2023 04:15
To: rob(a)jarratt.me.uk <mailto:rob@jarratt.me.uk> ; Rob Jarratt via cctalk
<cctalk(a)classiccmp.org <mailto:cctalk@classiccmp.org> >
Subject: Re: [cctalk] VT100: Failing 2114 Chip Replaced With One With The
Same Fault
Many thanks for the suggestion. This hadn't crossed my mind, so I checked. All the
things that I could identify on the schematic that connect to the bus (UART, interrupt
vector, flag buffer and modem signals) seem not to be enabled. I have looked at what is
sinking the data bus, there is a buffer which seems to be OK and the 8251 PIC. The PIC is
harder to check but I can see it is not selected and the input pins don’t appear to be
shorted.
Not really sure what else to consider.
On 10/07/2023 5:35 PM CDT Rob Jarratt via cctalk
<cctalk(a)classiccmp.org <mailto:cctalk@classiccmp.org> >
wrote:
I find this really hard to explain. It can't be the chip selection
logic because then the addresses 0x2400-0x2407 would also fail and I
checked the CS signal with the logic analyser just to be sure. I also
checked the address lines directly on the RAM chip for any stuck bits
and they seemed fine too.
What are the chances of two 2114 chips failing at exactly the same address?
Is there some failure mode I might not be considering?
Rob
Perhaps it isn't the 2114 or its associated circuit at all. Maybe some other
device is being incorrectly selected by that address and driving (half) the bus
low? Just a thought.
Will
If you want to build a ship, don't drum up people to collect wood and don't
assign them tasks and work, but rather teach them to long for the endless
immensity of the sea.
Antoine de Saint-Exupery
9 Oct
9 Oct
7:05 a.m.
New subject: VT100: Failing 2114 Chip Replaced With One With The Same Fault
On 2023-10-08 10:34, Rob Jarratt via cctalk wrote:
Put a scope on the data bus. You should see it, if two chips are driving
the bus at the same time ...
Perhaps it
isn't the 2114 or its associated circuit at all. Maybe some other
device is being incorrectly selected by that address and driving (half) the bus
low? Just a thought.
Many thanks for the suggestion. This hadn't crossed my mind, so I checked. All the
things that I could identify on the schematic that connect to the bus (UART, interrupt
vector, flag buffer and modem signals) seem not to be enabled. I have looked at what is
sinking the data bus, there is a buffer which seems to be OK and the 8251 PIC. The PIC is
harder to check but I can see it is not selected and the input pins don’t appear to be
shorted.
412
days inactive
413
days old
4 comments
3 participants
participants (3)
-
Adrian Godwin -
emanuel stiebler -
Rob Jarratt