Hi all, I have an ASUS Z590M-PLUS motherboard with an Intel i9-11900K processor, running Debian 11.6.0, 64 bit. The mobo has one on-board RS-232 port in the form of pin headers, 2x5 with the missing key-pin which connects to a 2.54mm 2x5 IDC connector and a DB-9 male (all standard stuff).

However, I cannot seem to find the port device. I have /dev/ttyxxx galore, as well as /dev/ttyUSBn and /dev/ttyACMn if I plug in USB to serial cables, as well as /dev/ttyS0 thru S3 ports.

But, none of them are the motherboard port. I test by using MINICOM to open a port, then check for serial activity on the DB-9 with an oscilloscope. I also short TxD and RxD together to see if pressed keys echo. None of the ports that I can open as serial devices activate the mobo port. Note that flow control is off, so it's not an RTS/CTS or XON/XOFF problem.

I DO have the port enabled in the BIOS, and it's got "DOS-like" parameters (i.e. address 0x3F8, IRQ-4).

Any ideas what I need to do to make this port work? It's not "life or death", but since the port is there, I'd like to be able to use it (to control a Kenwood HF transceiver).

Thanks!

Sorry folks, I'm an idiot. The problem was that my pin header to DB-9 cable was miswired. I thought it was like my old motherboard, that is, straight through.

After RTFM, I found the proper pinout, made a new cable and ta-da! it works.

Sorry if I wasted any of your time.

BTW, the port is /dev/ttyS0 as it should be.

Nobody here hasn't had a moment ...