- Omega Real-Time Clock Users' Guide

4.4 SETPOINT (ALARMS) WIRING

SETPOINT PLUG-IN CARD TERMINALS

SINKING OUTPUT LOGIC CARD

SOURCING OUTPUT LOGIC CARD

4.5 SERIAL COMMUNICATION WIRING

RS232 Communications

RS232 is intended to allow two devices to communicate over distances up to

50 feet. Data Terminal Equipment (DTE) transmits data on the Transmitted Data

(TXD) line and receives data on the Received Data (RXD) line. Data Computer

Equipment (DCE) receives data on the TXD line and transmits data on the RXD

line. The meter emulates a DTE. If the other device connected to the meter also

emulates a DTE, the TXD and RXD lines must be interchanged for

communications to take place. This is known as a null modem connection. Most

printers emulate a DCE device while most computers emulate a DTE device.

Some devices cannot accept more than two or three characters in succession

without a pause in between. In these cases, the meter employs a busy function.

As the meter begins to transmit data, the RXD line (RS232) is monitored to

determine if the receiving device is “busy”. The receiving device asserts that it

is busy by setting the RXD line to a space condition (logic 0). The meter then

suspends transmission until the RXD line is released by the receiving device.

RS485 Communications

The RS485 communication standard allows the connection of up to 32

devices on a single pair of wires, distances up to 4,000 ft. and data rates as high

as 10M baud. The same pair of wires is used to both transmit and receive data.

RS485 is therefore always half-duplex, that is, data cannot be received and

transmitted simultaneously.

Terminal Block Connection Figure

Extended Comms Connection Figure