Titan Electronics NCOM SERIAL 4XX Series, Руководство пользователя

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3.5 RS-422/485 Termination Resistors Option for NCOM-
413/NCOM-412
In some critical environments, when transmitted RS-422/485 signals arrive at the end
of a cable, they are reflected. This causes the signals to travel on the cable more than
once, which is called ringing. This can cause false reading of transmitted data. For long
cables, termination resistors are required. These increase the damping in order to
reduce reflections. The value of the termination resistor must match the impedance
of the cable, which is typically 120Ω. Generally, this must be done in the cabling, since
this depends on the installation of connections. Before applying the option, check your
cable specification for proper impedance matching.
Inside NCOM-413/NCOM-412, there are eight 3-pin 2.54mm pitch header blocks
(JP3~JP10) for jumper caps to enable TxD, RxD 120Ω termination resistors and eight
3-pin 2mm pitch header blocks (J2~J9) for jumper caps to enable TxD 750Ω biasing
resistors. You will need to open up the case and set the jumper settings for RS-422
mode or RS-485 mode, as per the requirements of your application.
Termination must not be installed in the middle of the cable. It is only permit ted at
both ends. Since a computer controlled serial port is almost always at one end of the
cable, termination is disabled by default.
Biasing of data lines must only occur at a single point anywhere in the cabling.
NCOM-413/NCOM-412 provides biasing for ease of installation. If your cabling
doesn’t provide biasing, please be sure to enable this inside the unit.
Settings are listed as follows:
3-pin Header for Termination Option Configuration
Serial Port 1
Jumper Function
JP3 1-2 Enable Enable TxD+/- 120Ω termination resistor.
2-3 Disable Disable TxD+/- 120Ω termination resistor.
JP4 1-2 Enable Enable RxD+/- 120Ω termination resistor.
2-3 Disable Disable RxD+/- 120Ω termination resistor.
Jumper Function
J2 1-2 Enable Enable TxD+ pull-high 750Ω biasing resistor.
2-3 Disable Disable TxD+ pull-high 750Ω biasing resistor.
J3 1-2 Enable Enable TxD- pull-low 750Ω biasing resistor.
2-3 Disable Disable TxD- pull-low 750Ω biasing resistor.