Its serial communication
Func DB-9 PIN# DB25 pin#
Rec Data 2 3
Trans data 3 2
Clear send 8 5
Request send 7 4
Data set ready 6 6
Signal ground 5 7
Data term ready 4 20
Data carrier 1 8

now sometimes I had "short not really" on a db9 pins pins 7 and 8 or others.
this was to tell the PC to send the data even if the machine wasn't "ready"
You have to play with baud rates to get it to go smooth. I will see if I can
find my notes on what pins I had to wire to each other.