Red Lion TCU - Manual (Page 62)

Terminal Emulation Program For IBM ® PC (Cont’d)
If an RS485 card cannot be obtained, and only an RS232 port is available,
the Red Lion Controls GCM232 & GCM422 converter modules can be used.
The GCM232 converts from RS232 to 20 mA current loop. The GCM422
converts the 20 mA current loop to RS422/RS485. A male 25 pin D connector
is required to interface the GCM422 to the unit.
Note: The GCM422 requires the TX EN terminal for proper operation. The
availability of the TX EN terminal is model dependent. If TX EN terminal is not
shown on unit label, it is not available for that model.
Serial Connections
When wiring the terminal block at the rear of the unit, refer to the label with
the terminal description for installing each wire in its proper location. It is
r e c o mme n d e d t h a t s h i e l d e d ( s c r e e n e d ) c a b l e b e u s e d f o r s e r i a l
communications. This unit meets the EMC specifications using Alpha #2404
cable or equivalent. There are higher grades of shielded cable, such as four
conductor twisted pair, that offer an even higher degree of noise immunity.
Only two transceiver wires and a common are needed.
The two data (transceiver) wires connect to the TX/RX(+) and TX/RX(-)
terminals, appropriately.
Th e cable should consist o f a shielded twisted p air and in some
applications a signal ground may be required to establish a ground reference.
The signal ground is required if the equipment does not have internal bias
resistors connected to the RS485 transceiver lines. The signal ground is
connected at the RS485 common of only one TCU unit to the RS485
equipment. If necessary, the shield can be used as the signal ground.
The signal input common is isolated from the RS485 common and the
analog output “-” terminal.
Note: Do not connect any of the commons to the analog output “-” terminal.
Terminal Descriptions
RS485 COMM. - Common may be required for communication hook-up.
TX/RX(+) & TX/RX(-) - The TCU transmits and receives on these two
terminals which are connected to the external device.
TX EN. - Used with a Red Lion Controls (RLC) GCM422 Serial Converter
Module (RS422 to 20 mA Loop). Otherwise not normally used.
Note: Some models do not have TX EN. This is an output used in conjunction with
interface converter Model GCM422, to convert RS485 to 20 mA current loop.
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Figure 24, Computer Interface