Sel SEL-787 - Page 290

7.2
SEL-787 Relay Instruction Manual Date Code 20150130
Communications
Communications Interfaces
Serial (EIA-232 and
EIA-485) Port
Use the EIA-232 port for communications distances of 15 m (50 feet) in low
noise environments. Use the optional EIA-485 port for communications
distances 1200 m (4000 feet) maximum distance (to achieve this
performance, ensure proper line termination at the receiver).
To connect a PC serial port to the relay front-panel serial port and enter relay
commands, you will need the following:
➤ A personal computer equipped with one available EIA-232
serial port
➤ A communications cable to connect the computer serial port to
the relay serial ports
➤ Terminal emulation software to control the computer serial port
➤ An SEL-787 Relay
Some of the SEL devices available for integration or communication system
robustness are included in the following list:
➤ SEL Communications Processors (SEL-2032, SEL-2030,
SEL-2020)
➤ SEL-2800 Series Fiber-Optic Transceivers
➤ SEL-2890 Ethernet Transceiver
➤ SEL-3010 Event Messenger
➤ SEL-2505 SEL Remote I/O Module (with the SEL-2812
compatible ST option only for fiber-optic link to Port 2)
A variety of terminal emulation programs on personal computers can
communicate with the relay. For the best display, use VT-100 terminal
emulation or the closest variation.
The default settings for all EIA-232 serial ports are listed below:
➤ Baud Rate = 9600
➤ Data Bits = 8
➤ Parity = N
➤ Stop Bits = 1
To change the port settings, use the SET P command (see Section 6: Settings)
or the front-panel. Section 8: Front-Panel Operations provides details on
making settings with the front panel.
Hardware Flow Control
All EIA-232 serial ports support RTS/CTS hardware handshaking (hardware
flow control). To enable hardware handshaking, use the SET P command or
front-panel
PORT submenu to set RTSCTS = Y. Disable hardware handshaking
by setting RTSCTS := N.
➤ If RTSCTS := N, the relay permanently asserts the RTS line.
➤ If RTSCTS := Y, the relay deasserts RTS when it is unable to
receive characters.
➤ If RTSCTS := Y, the relay does not send characters until the
CTS input is asserted.
Fiber-Optic Serial
Port
Use the optional fiber-optic port (PORT 2) for safety and communications
distances as far as 1 km. Communications distances as far as 4 km can be
achieved by using an SEL-2812 transceiver on PORT 3. While PORT 2 and
the SEL-2812 are compatible, PORT 2 is less sensitive than the SEL-2812,
which limits the distance to 1 km.