| Odd Serial communications issue [message #397255] |
Thu, 30 July 2020 13:22  |
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Originally posted by: Henry Pedro
Cross post from FB group because "look eBay sale" is way more "relevant" than a boring technical issue.
I've got a funny serial communications issue with a clone II+.
The clone seems to otherwise work properly, but serial communications via the Super Serial Card are not working.
The SSC is known to be good - works fine in other machines, both clone and genuine II+.
On this particular clone it receives communications, both from a modem (Ascii Express) and from a modern PC via ADTPro.
But the Apple Clone won't send data out via the SSC.
It won't query the modern PC via ADTPro and can't talk to a modem in Ascii Express. Yes I have verified all settings and dip switches, and this card (and Ascii Express & ADTPro) work properly in another clone and genuine II+.
So I suspect some sort of data bus issue to the slots (doesn't matter if I move the SSC to slot 4 - it still won't work).
Anyone who's familiar with the II+ architecture can point me in the right direction?
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| Re: Odd Serial communications issue [message #397275 is a reply to message #397255] |
Thu, 30 July 2020 21:07  |
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Originally posted by: James Davis
On Thursday, July 30, 2020 at 10:22:53 AM UTC-7, Henry Pedro wrote:
> Cross post from FB group because "look eBay sale" is way more "relevant" than a boring technical issue.
>
> I've got a funny serial communications issue with a clone II+.
> The clone seems to otherwise work properly, but serial communications via the Super Serial Card are not working.
> The SSC is known to be good - works fine in other machines, both clone and genuine II+.
> On this particular clone it receives communications, both from a modem (Ascii Express) and from a modern PC via ADTPro.
> But the Apple Clone won't send data out via the SSC.
> It won't query the modern PC via ADTPro and can't talk to a modem in Ascii Express. Yes I have verified all settings and dip switches, and this card (and Ascii Express & ADTPro) work properly in another clone and genuine II+.
> So I suspect some sort of data bus issue to the slots (doesn't matter if I move the SSC to slot 4 - it still won't work).
> Anyone who's familiar with the II+ architecture can point me in the right direction?
Check the continuity/resistance of the 16 Address traces and the 8 Data traces all the way from the 6502 to the SSC. You are looking for breaks in the traces, which would cause infinite resistance, an open circuit. It can happen at the slot connectors, too, if they are dirty, which may cause finite resistance that is too high for the signal to be seen. You can also check voltages when the computer is powered up and running, but they may change too fast to see with a multimeter, so you would need an oscilloscope to really do a thorough check. If you do not have proper voltages right at the 6502, then the microprocessor or its socket connections are bad.
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| Re: Odd Serial communications issue [message #397284 is a reply to message #397255] |
Fri, 31 July 2020 03:02 |
spectrumdaddy
Messages: 191
Registered: November 2012
Karma: 0
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Senior Member |
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Henry Pedro <can7700@gmail.com> wrote:
> It won't query the modern PC via ADTPro and can't talk to a modem in Ascii
> Express. Yes I have verified all settings and dip switches, and this card
> (and Ascii Express & ADTPro) work properly in another clone and genuine
> II+. So I suspect some sort of data bus issue to the slots (doesn't matter
> if I move the SSC to slot 4 - it still won't work). Anyone who's familiar
> with the II+ architecture can point me in the right direction?
It sounds as if the hardware handshake to the serial port is not
working. I doubt if it would be the data bus itself, as then the
firnware on the card would not work at all.
Are you using the same serial cable as you did in the other machines?
Check all the handshake pins on the DB-25 connector. have continuity
Cheers - Ewen
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| Re: Odd Serial communications issue [message #397325 is a reply to message #397284] |
Sat, 01 August 2020 07:39 |
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Originally posted by: Henry Pedro
On Friday, July 31, 2020 at 4:02:28 AM UTC-3, Ewen wrote:
> Henry Pedro <can7700@gmail.com> wrote:
>
>> It won't query the modern PC via ADTPro and can't talk to a modem in Ascii
>> Express. Yes I have verified all settings and dip switches, and this card
>> (and Ascii Express & ADTPro) work properly in another clone and genuine
>> II+. So I suspect some sort of data bus issue to the slots (doesn't matter
>> if I move the SSC to slot 4 - it still won't work). Anyone who's familiar
>> with the II+ architecture can point me in the right direction?
>
> It sounds as if the hardware handshake to the serial port is not
> working. I doubt if it would be the data bus itself, as then the
> firnware on the card would not work at all.
>
> Are you using the same serial cable as you did in the other machines?
> Check all the handshake pins on the DB-25 connector. have continuity
>
> Cheers - Ewen
I've done that. The card and cables all work properly in another Apple II+.
James Davis might be on to something.
Whatever is broken is affecting all the slots (well, at least slot 2 and slot 4 which are the two slots I tested the card.)
But if it is a broken data bus line why is the computer receiving data but not sending? Perhaps an address bus?
Is there a circuit between the CPU and the slots that govern whether data is sending or receiving?
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| Re: Odd Serial communications issue [message #397346 is a reply to message #397325] |
Sat, 01 August 2020 20:43 |
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Originally posted by: James Davis
On Saturday, August 1, 2020 at 4:39:26 AM UTC-7, Henry Pedro wrote:
> On Friday, July 31, 2020 at 4:02:28 AM UTC-3, Ewen wrote:
>> Henry Pedro <...@gmail.com> wrote:
>>
>>> It won't query the modern PC via ADTPro and can't talk to a modem in Ascii
>>> Express. Yes I have verified all settings and dip switches, and this card
>>> (and Ascii Express & ADTPro) work properly in another clone and genuine
>>> II+. So I suspect some sort of data bus issue to the slots (doesn't matter
>>> if I move the SSC to slot 4 - it still won't work). Anyone who's familiar
>>> with the II+ architecture can point me in the right direction?
>>
>> It sounds as if the hardware handshake to the serial port is not
>> working. I doubt if it would be the data bus itself, as then the
>> firnware on the card would not work at all.
>>
>> Are you using the same serial cable as you did in the other machines?
>> Check all the handshake pins on the DB-25 connector. have continuity
>>
>> Cheers - Ewen
>
> I've done that. The card and cables all work properly in another Apple II+.
> James Davis might be on to something.
> Whatever is broken is affecting all the slots (well, at least slot 2 and slot 4 which are the two slots I tested the card.)
>
> But if it is a broken data bus line why is the computer receiving data but not sending? Perhaps an address bus?
> Is there a circuit between the CPU and the slots that govern whether data is sending or receiving?
Search for SAMS (Publisher) Apple II Troubleshooting and Repair Guide.
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| Re: Odd Serial communications issue [message #397356 is a reply to message #397325] |
Sun, 02 August 2020 02:48 |
spectrumdaddy
Messages: 191
Registered: November 2012
Karma: 0
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Senior Member |
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Henry Pedro <can7700@gmail.com> wrote:
> But if it is a broken data bus line why is the computer receiving data but
> not sending? Perhaps an address bus? Is there a circuit between the CPU
> and the slots that govern whether data is sending or receiving?
The address bus is common to all the functions on the card, and common
to all the other slots as well, and has nothing directly to do with
sending or receiving, as the Read/Send functions are entirely on the SSC
card itself.
The Send/Read functions are called up by the software you are running to
the firmware on the card.
Does the card Send in any of the other slots? Do cards in other slots
work properly?
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| Re: Odd Serial communications issue [message #397430 is a reply to message #397356] |
Mon, 03 August 2020 21:00 |
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Originally posted by: Henry Pedro
On Sunday, August 2, 2020 at 3:48:33 AM UTC-3, Ewen wrote:
> Henry Pedro <can7700@gmail.com> wrote:
>
>> But if it is a broken data bus line why is the computer receiving data but
>> not sending? Perhaps an address bus? Is there a circuit between the CPU
>> and the slots that govern whether data is sending or receiving?
>
> The address bus is common to all the functions on the card, and common
> to all the other slots as well, and has nothing directly to do with
> sending or receiving, as the Read/Send functions are entirely on the SSC
> card itself.
>
> The Send/Read functions are called up by the software you are running to
> the firmware on the card.
>
> Does the card Send in any of the other slots? Do cards in other slots
> work properly?
That's the mystery. Other cards in the computer work properly. Parallel printer card, memory (16 K) card, drive controller, 80 column card all work in their assigned slots. The SSC itself works in another machine.
The SSC does not work in the two slots I tried it. It didn't work in slot 2 and didn't work in slot 4.
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| Re: Odd Serial communications issue: SOLVED! [message #397433 is a reply to message #397356] |
Mon, 03 August 2020 21:06 |
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Originally posted by: Henry Pedro
I found the issue. And thanks to James Davis that suggested I ring out all the traces on the slots.
It also took an RS232 monitor card (one of those little boxes that shows which RS232 signals are on and off with LEDs).
It was showing TxD as "on" even though there was no communication and no terminal software running. Also a giveaway was that DTR and CTS were also on - signals generated by the computer.
This led to a bad/missing -12V line.
The SSC requires the presence of -12V to generate the correct RS232 signals.
Everything worked with a replacement power supply.
Power supply repairs are pending.
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