[51] max 485 in noisy environment

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unbhandari

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i am working with max485 for rs 485 4 wire system with modbus protocol. i found loss in serial connection when ac servo drive goes on. can any one help in this regards?
 

4 wire RS485?
Do you have power supply for the circuit in the cable too?
 

is it full duplex mode??
you must use 120 ohm resister between differential line.
 

Since you said you used a MAX485 driver, I assumed you used half duplex, since that driver is a half duplex driver only.

If you have 4 wires and want to use a full duplex communication you may need to switch driver chip.

If it is full duplex RS485 you need to terminate with 4 x 120 ohm resistors, 2 resistors in each end of the cable.
 

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