If I understand what each person has said, we have three conflicting pieces of advice. Maybe someone who understands the big picture can explain why all three approaches are correct...

I do know that the machine worked with 25 pins (on both sides) at one time. This machine came from a school where I was a student a number of years ago, and it was set up using the 25 pin port on the PC then.

Incidentally, I'm not interested in DNC (drip feed) just yet. I will want to do this, but getting simple file transfers to work is a first step.

Update: I followed the instructions of the pdf given by Al_The_Man, and it didn't work. It doesn't matter whether the cable is wired with or without "full handshake" (i.e., whether pins 4 and 5 are jumpered or pass through after swapping). The pdf says to change param 0002 to 0000 0001 (it was 1000 0001), and change I/O to 0 (it was 2). When I did that and tried to receive a program, FANUC gives me alarm 086. When I changed these two values back, the alarm goes away. It still doesn't accept the download, but no alarm.