Null Modem cable wiring

Atari 850 / ICD P:R: to 9 pin PC port

Atari 850 to PC Null Modem (DB9-DB9)

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)

Atari 850 to PC Null Modem (DB9-DB25)

Note: The original MIO interface has the same pinout as the Atari 850. The later remakes are following the standardized PC scheme.


9 pin PC port to 9 pin PC port (software handshake required)

PC Null Modem, no handshaking (DB9-DB9)

PC Null Modem, no handshaking (DB9-DB9)


9 pin PC port to 9 pin PC port (hardware handshake)

PC Null Modem, hardware handshaking (DB9-DB9)

PC Null Modem, hardware handshaking (DB9-DB9)


9 pin PC port to 25 pin PC port (software handshake required)

PC Null Modem, no handshaking (DB9-DB25)

PC Null Modem, no handshaking (DB9-DB25)


9 pin PC port to 25 pin PC port (hardware handshake)

PC Null Modem, hardware handshaking (DB9-DB25)

PC Null Modem, hardware handshaking (DB9-DB25)


25 pin PC port to 25 pin PC port (software handshake required)

PC Null Modem, no handshaking (DB25-DB25)

PC Null Modem, no handshaking (DB25-DB25)


25 pin PC port to 25 pin PC port (hardware handshake)

PC Null Modem, hardware handshaking (DB25-DB25)

PC Null Modem, hardware handshaking (DB25-DB25)


TD (TX) ⇒ Transmitted Data (Transmit)
RD (RX) ⇐ Received Data (Receive)
RTS ⇒ Request To Send
CTS ⇐ Clear To Send
DSR ⇐ Data Set Ready
DTR ⇒ Data Terminal Ready
CD (DCD) ⇐ Carrier Detect (Data Carrier Detect)
RI ⇐ Ring Indicator
GND = common GrouND

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