Marsh PatrionPlus, Technical Manual

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RS-232
29669/02080 Rev AG
C - 3
Cabling Requirements When connecting an external device to the RS-232 connector on your
PatrionPlus controller, you must use the correct cabling. If you do not,
RS-232 communication will not be possible. The cabling that you need
depends on the classification of your external device (DCE or DTE) and the
gender and size of the RS-232 port on the device.
The PatrionPlus controller is classified as DCE (data communications
equipment). DCE provides the functional requirements to establish,
maintain, and terminate the connection with the device it is communicating
with. DCE also sends information or commands properly coded for the
receiving device.
DTE (data terminal equipment) typically receives information and
commands from other devices, stores information, and controls yet other
devices.
DCE and DTE equipment can easily communicate with each other.
However, your PatrionPlus DCE can also communicate with other DCE
equipment. Specific cabling is required for each possibility.
To determine your cabling requirements, first determine the classification of
your external device (see the manufacturer’s technical documentation). If
you will be connecting to a DTE, use a “straight-through” cable. (See
Figure CA.) If you will be connecting to another DCE, use a null modem.
(Any prewired, off-the-shelf null modem is acceptable.) Lastly, make sure
the cable is compatible—in size and gender—with the connector on the
external device and on the PatrionPlus controller, which is a DB25 female
connector.
Figure CA: RS-232 Communication “Lines” and Possible Configurations
RXD 2
TXD 3
SG 7
TXD
RXD
SG
RXD 2
TXD 3
SG 7
RXD
TXD
SG
Patrion
(DCE)
Patrion
(DCE)
Null Modem
Configuration
Straight-Through
Configuration
External Device
(DCE)
External Device
(DTE)