Date Code 20080110 Communications 7-3
SEL-387E Instruction Manual
Physical Layer
The SEL-387E provides EIA-232 and EIA-485 physical layers for serial communications as
shown below:
• Three EIA-232 serial ports:
One EIA-232 port on the front
Two EIA-232 ports on the rear
• One EIA-485 port on the rear
Connect the serial port to a computer serial port for local communications or to a modem for
remote communications.
All EIA-232 serial ports support RTS/CTS hardware handshaking. RTS/CTS handshaking is not
supported on the EIA-485 Serial Port 1. To enable hardware handshaking, use the SET P
command (or front-panel SET pushbutton) to set RTSCTS = Y. Disable hardware handshaking
by settings RTSCTS = N.
• If RTS_CTS = N, the relay permanently asserts the RTS line.
• If RTS_CTS = Y, the relay desasserts RTS when it is unable to receive characters
• If RTS_CTS = Y, the relay does not send characters until the CTS input is asserted.
The serial port interfaces (DB-9 connectors and screw-terminal connector) support a
communications interface, power supply for communications interface converters, and time
synchronization source (IRIG-B), as shown in
Table 7.1.
Table 7.1: Physical Interfaces
Port Communications
Interface
Demodulated
IRIG-B
+5 VDC Power
Supply
Port 1 EIA-485 X X
Port 2 EIA-232 X X
Port 3 EIA-232 X
Port 4 EIA-232
Figure 7.1 shows the serial port physical interfaces (connectors) on the relay rear panel.
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