there were many incompatible serial pinouts, just like with later usb
you can trace header to the pins of nearby chips (voltage translators for rs232)

jpolster2022 wrote on 2022-11-29, 05:14:

I have an Intel Advanced / ZP Motherboard with the 256k Cache running MR BIOS. Serial ports are not working. I purchased this board as NOS from eBay and I need working serial ports to use a mouse. I believe I am attaching the headers to the IDC10 Plugs correctly however windows will not detect my serial mice. I find it hard to believe that both serial ports are non functional. I have tried different headers as well. one from an old Gateway 486 and one from eBay

I have try 10-12 headers before get compatible with original Intel desktop.

The manual shows the pinout. No need to test. The pinout matches the Intel / DTK Standard. I don't know what my headers are but im assuming they are Intel / DTK as they came from a 486 Gateway and the internet.