Red-lion TCU User Manual download pdf (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

recommended that shielded (screened) cable be used for serial

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 o f 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.

The cable should consist of a shielded twisted pair and in some

applications a signal ground may be required to establish a g round 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.

Figure 24, Computer Interface

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Red-lion TCU User Manual Page 62