Null Modem cable wiring
Atari 850 / ICD P:R: to 9 pin PC port

Atari 850 to PC Null Modem (DB9-DB9)
Atari 850 / ICD P:R: to 25 pin PC port

Atari 850 to PC Null Modem (DB9-DB25)
Note: The original MIO interface has the same pinout as the Atari 850. The later remakes • • • » read more »
People’s Thoughts