DISCUSSION

Introduction
Maptech, through it's Captn. Jack's subsidiary, offers two cables for connecting serial GPS units to the 9-pin serial connection on a PC. Making the connection requires knowing which wire is to be connected to the transmit and receive connections for the GPS and/or Autopilot.

Terminology
NMEA connections (or the connections from your GPS) may not indicate "Transmit" or "Receive." They may be labeled NMEA IN or NMEA OUT. Moreover, they may also indicate Positive (+) and Negative (-) connections.

For the sake of the explanation below, we will use the Transmit/Receive terms used in Serial communications. Thus, a wire or connection on your GPS/AP that is labeled "NMEA IN" or "NMEA IN +" is the "Receive" connection for that device. A wire or connection on your GPS/AP that is labeled "NMEA OUT" or "NMEA OUT +" is the "Transmit" connection for that device. A wire or connection on your GPS/AP that is labeled "NMEA - (IN or OUT)" is the "Ground" connection for that device.

Connections - Opto Isolator Cable
Yellow:
The yellow wire is the Positive (+) Receive (or In) connection for the computer. Connect it to the Positive (+) NMEA Transmit (or Out) connector on the GPS. This allows the GPS to transmit its data to be received by the computer (on pin 2 of the DB9 connector.)

Green:
The green wire is the Ground/Negative (-) Receive connection for the computer. Connect it to the Ground/Negative (-) NMEA Transmit (or Out) connector on the GPS. This completes the circuit that allows the GPS to transmit its data to be received by the computer (on pin 5 of the DB9 connector.)

Red:
The red wire is the Positive (+) Transmit (or Out) connection for the computer. Connect it to the Positive (+) NMEA Receive (or In) connector on the GPS or Autopilot. This allows the computer (via pin 3 of the DB9 connector) to transmit its data to be received by the GPS or Autopilot.

Black:
The black wire is the Ground/Negative (-) Transmit (or Out) connection for the computer. Connect it to the Ground/Negative (-) NMEA Receive (or In) connector on the GPS or Autopilot. This allows the computer (via pin 5 of the DB9 connector) to transmit its data to be received by the GPS or Autopilot.

Connections - CAPN GPS/Serial Cable CA-100H
Black:
The black wire is the Positive (+) Receive (or In) connection for the computer. Connect it to the Positive (+) NMEA Transmit (or Out) connector on the GPS. This allows the GPS to transmit its data to be received by the computer (on pin 2 of the DB9 connector.)

Green:
The green wire is the Ground/Negative (-) connection for the computer. Connect it to the Ground/Negative (-) NMEA connector on the GPS or Autopilot. This completes the circuit that allows the GPS to transmit its data to be received by the computer (on pin 5 of the DB9 connector) and for the Autopilot to receive data from the computer.

White:
The white wire is the Positive (+) Transmit (or Out) connection for the computer. Connect it to the Positive (+) NMEA Receive (or In) connector on the GPS or Autopilot. This allows the computer (via pin 3 of the DB9 connector) to transmit its data to be received by the GPS or Autopilot.

Related Technical Documents
Serial COM Port Pin Assignments for GPS and Autopilot Connections
Connecting a GPS to a USB port
GPS and Computer Communications - HyperTerminal Test
How do I "share" a GPS between two (or more) different applications?