Modbus line terminator RS485 RJ45 connector

Modbus terminator RJ45 connector

VE.Can Ethernet terminator

Modbus Line Termination

VE.Can RJ45 terminator

This line termination enables your product integration in Modbus serial link connection. 

It has a 120Ohm resistance and RJ45 connection type.

Terminator Capacitance    1 nF

Terminator Resistance    120 Ohm

Communication Port Protocol    Modbus

The Modbus cable communication pair has an impedance of 120 Ω or 150 Ω. 

The Modbus master is at one end of the Modbus cable and usually has a switchable termination impedance. 

At the other end of the Modbus cable, a Modbus line termination with an impedance of 120 Ω or 150 Ω must be connected.

The Modbus cable must therefore be terminated at each end by a Modbus line termination with an impedance of 120 Ω or 150 Ω.

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Termination resistance is an obstacle encountered in the transmission process of electronic information.

When high-frequency signal is transmitted, the signal wavelength is shorter than that of the transmission line, and the signal will form a reflected wave at the end of the transmission line, which will interfere with the original signal. Therefore, it is necessary to add a terminal resistance at the end of the transmission line so that the signal does not reflect after reaching the end of the transmission line.

In long-line signal transmission, in order to avoid signal reflection and echo, it is also necessary to connect a terminal matching resistor at the receiving end.

Termination resistors: resistors connected in parallel to a pair of communication lines at both ends of the line network (on the two communication ports farthest apart).

According to transmission line theory, terminating resistors can absorb reflected waves on the network, effectively enhancing signal strength.

The value of the two terminating resistors in parallel should be substantially equal to the characteristic impedance of the transmission line at the communication frequency.

Its termination matching resistance value depends on the impedance characteristics of the cable and has nothing to do with the length of the cable.

RS-485/RS-422 is generally connected by twisted pair (shielded or unshielded), and the terminal resistance is generally between 100 and 140Ω, and the typical value is 120Ω.

In the actual configuration, a terminal resistor is connected to each of the two terminal nodes of the cable, that is, the nearest end and the farthest end, while the node in the middle part cannot be connected to a terminal resistor, otherwise it will cause communication errors.

The role of terminating resistors

1) General statement: The terminal resistance is to weaken the signal reflection in the communication cable

(2) The signal transmission circuit has its characteristic impedance (about 120Ω in terms of Twisted Pair) due to various transmission lines.

When the signal is transmitted to the terminal in the transmission line, if its terminal impedance and characteristic impedance are different, it will cause reflection and distort the signal waveform (sag or bulge).

The distortion phenomenon is not obvious when the transmission line is short, but it will become more serious as the transmission line is lengthened, resulting in incorrect transmission. At this time, a Terminator must be installed.

A 120Ω terminal resistor is installed inside the FBs-PLC. To apply the terminal resistor, please open the PLC communication cover and turn the DIP switch to the “ON” position (the DIP switch is set to the “OFF” position at the factory), but pay attention to the terminal Resistors can only be applied to the PLCs on the leftmost and rightmost sides of the Bus. All PLC switches between the two sides should be placed in the “OFF” position, otherwise the RS-485 push capability will be insufficient.

A 485 network may have up to 32 devices connected, and the maximum line length is 1 km. Impedance matching resistors are used at both ends of the terminal load resistance line. Is all the resistances XXX ohms, or the equivalent resistance value of so many combined is 120 ohms

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