LabComm collects data from an analyser by connecting to a port on the analyser. This can be a LAN (RJ45), USB, or Serial (RS232) port.

The majority of analysers use serial ports to send and receive data from. Serial ports are also known as RS232 ports. RS232 ports can have different pins or connections within the port and this may require that a cable with specific pin configurations be made up. We can provide the correct serial cables. The end user who wants to interface to an analyser using LabComm would not need to worry about the cable configurations - we are providing this information for reference and guidance only.

There are several possible Null modem cable configurations. The “standard” pin outs are shown below.

9-Pin Connector

RXD pin 2   ----------------------------------------       TXD    pin 3 
TXD pin 3   ----------------------------------------       RXD    pin 2 
DTR pin 4  ----------------------------------------------- DSR    pin 6 
GND pin 5 ----------------------------------------        GND    pin 5
DCD pin 1  ----------------------------------------        DTR    pin 4 
RTS  pin 7   ----------------------------------------      CTS    pin 8 
CTS  pin 8 ------------------------------------------      RTS    pin 7

This can also be displayed in a graphical format:

  • Simple null modem without handshaking

We can start with this cable. It is the simplest to understand as there are only three lines in use - the signal ground and the transmit and receive data lines. This means that one wire transmits the data, a different wire sends the data and one wire acts as the signal ground

 Thumbnail image


  • Null modem with loop back handshaking

This is the nearest to a “standard” and matches the pinout drawing first shown. This is used for the majority of analysers.


Serial null modem

  • Null modem with partial handshaking

Serial null modem partial

  • Null modem with full handshaking

Serial null modem full

The original pin layout for RS232 was developed for a 25 pin D sub connector. With this pinout configuration provisions were made for a secondary communication channel. In practice, only one communication channel with accompanying handshaking is present. For that reason, as well as the move towards miniaturisation the smaller 9 pin version is much more commonly used today.

Note: The protective ground is assigned to a pin at the large connector, in DB9 version protective ground connector to the enclosure.

LabComm will supply the correct serial cable for each analyser we interface to. We use a 9 pin connector as standard for the computer end.