Beckhoff EtherCAT EL6001, Документация

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Product overview
EL600x, EL602x 15 Version: 4.6
Level interfaces
The EL6001/6002 devices operate at an RS232 level with reference to GND, the EL6021/6022 devices with
a differential RS485/422 level.
Fig. 9: Level interfaces RS232, RS485/422
Termination and topology
The serial RS422 and RS485 communication technologies operate with voltage levels on a 2-wire line.
Reflections at high-resistance line ends can lead to signal distortion. For this reason termination resistors are
required at the receiver. For RS422/485 these are 120 Ω resistors, which together with the line resistance
result in a voltage drop over the transmission link.
Permitted cable length
The line resistance together with the termination resistor results in an overall voltage drop over the
transmission link. An unacceptably high number of termination resistors would result in excessive
attenuation of the signal.
The system design should ensure that the voltage does not drop below 200 mV at the receiver (see
Fig. ), which is the minimum voltage required.
In RS422 mode each line must be terminated with 120 Ω at the receiver.
Fig. 10: RS422 termination
In RS485 mode with several devices, termination resistors are only used at the two end devices.