Null modem or straight through serial converter?

[kylejams]

IBM "Ping master" model no. 6113442

I'm kind of new to vintage keyboards, and I don't know much about legacy serial ports. My PC and my pingmaster seems to have male 9-pin serial port connectors, although the pingmaster is only utilizing 4 pins, while the rest of the five are empty. So I thought since I had a serial port on my PC motherboard that I wouldn't have to go around fishing for an expensive converter to USB; however, I did need a female to female serial port connector to connect them. I'm given two choices to buy a null modem or a straight through female to female. I bought a straight through, and I think I made the wrong choice because it's not working. Can someone verify whether I need a null modem or straight through because I really want to plug this in my serial port.

[ErgoMacros]

Hi,
First I'll answer your question, then I'll tell you what you need to connect the keyboard to use it.

To get the electrical signals / wires to talk you need the Keyboard transmit to go to the PC receive, and vice versa. Unfortunately the pins used in the IBM keyboard don't match the now-standard 9-pin serial connectors. So neither will work. You could make a custom cable, BUT that, in the end, won't work either. See part #2.

Part #2:
Windows is  not expecting a keyboard of this type to be on your serial port. So even if you connect it electrically it won't know what to do.
You need a protocol converter and might as well go from your 4704 keyboard to USB. Hasu makes and sells these, or you can make your own.
Here's the start of the thread describing it:
      https://geekhack.org/index.php?topic=54706.msg1225701#msg1225701

And this thread had a "how to make one" video.
      https://geekhack.org/index.php?topic=54706.0

Hope that helps.