Serial Port not working

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Mar 19, 2022
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My PC has a 2014 A55M-E35 motherboard. This has a serial port connector JCOM1. Serial ports being ancient technology I have never used it. Now, after eight years, I need it to connect to a serial digitising pad. I therefore bought a serial/parallel DB9/DB25 back panel interface and plugged the DB9 into JCOM1.

It is apparently dead - with hardware handshaking disabled it won't communicate via a null modem cable with the digitising pad, and a simple loopback of connecting pins 2 & 3 with a terminal emulator produces nothing.

Device manager shows a COM1 and that it 'is working correctly'.

As it has never been used for eight years from new it seems unlikely it never worked - is there some trick to turning it on?

Any expertise gratefully received - thanks.
 

jakub-p2

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You have to look into the BIOS, sometimes such settings as serial are disabled by default.
 
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Thanks - good try.
Indeed, in the Bios is 'Settings | Advanced | Super IO Configuration | Serial (COM) Port0 Configuration | Serial (COM) Port0 |'
And after all that it said 'Enabled'.
As a forlorn hope I disabled it; saved and rebooted; enabled it; saved and rebooted. Still dead. Though the terminal emulator seems to be able to 'open COM1'.
Is there any way I can test it at the hardware level to determine if it is working?
'Enabled' has extra options, 'Auto' and 5 different IO hex addresses and associated IRQ lists - would it be any use changing to one of these?
 

jakub-p2

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Thanks - good try.
Indeed, in the Bios is 'Settings | Advanced | Super IO Configuration | Serial (COM) Port0 Configuration | Serial (COM) Port0 |'
And after all that it said 'Enabled'.
As a forlorn hope I disabled it; saved and rebooted; enabled it; saved and rebooted. Still dead. Though the terminal emulator seems to be able to 'open COM1'.
Is there any way I can test it at the hardware level to determine if it is working?
'Enabled' has extra options, 'Auto' and 5 different IO hex addresses and associated IRQ lists - would it be any use changing to one of these?
Nah, as usual auto is the way to go if You don't understand what these options are. Remember to change settings such as baud rate/parity bits/... in Windows for the COM ports to match your pad.
 
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Indeed I have set the comms parameters to match, but even if set wrongly it should still produce gibberish I think, if communicating?
 

jakub-p2

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Indeed I have set the comms parameters to match, but even if set wrongly it should still produce gibberish I think, if communicating?
Not really, computers aren't humans, communication on RS232 isn't even similar to language as we know it. Either there is a link or there isn't. RX could probably be measured with an oscilloscope, but first You would have to send instructions through it without a 'handshake'.
What else... drivers? signal integrity?
We have also an easy way out - CH340 RS232 to USB converter - I use that for my BGA rework station, works nicely, but works only on even parity and 7 data bits, baud rate 19.2; other setting won't result in a handshake.
 

jakub-p2

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Yes - that is something to be considered - irritating though that it is already on the motherboard - thanks.
Yeah, if installing chipset/pad drivers and fiddling more with COM settings doesn't work, then I'm terribly sorry, but I'm out of ideas.
 

Alan J T

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Yes - that is something to be considered - irritating though that it is already on the motherboard - thanks.
Yeah, if installing chipset/pad drivers and fiddling more with COM settings doesn't work, then I'm terribly sorry, but I'm out of ideas.
Com Port to USB adapter should work about $10 I guess if that much
1647926240273.png
 
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SOLVED

It turns out that there are two standards for motherboard serial header pin-outs. AT/Everex (new) and DTK/Intel (old). My MSI header is AT/Everex. Clearly I bought a DTK/Intel IDC10 to DB9 cable (they of course look identical, and sellers never mention which they are).
 
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