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ADM2587E RO problem

Question asked by sige on May 15, 2017
Latest reply on May 15, 2017 by sige

Hello

I'm using ADM2587E to implement a RS485 modbus and an slave. They can't work together. They work separately but not together.

I've analyzed the communication with a logical analyzer and it seems de problem is a little drop in voltage in RO pin of the receiver. The microcontroller sees that drop as a new start bit and it thinks it has received one extra byte. After that, CRC checking discards the message. I have attached two screenshots.

If I place a resistor (from 0R to 330R between common and A line, everything works properly and the voltage drop desappears.

Master has 560R bias resistors and a termination of 120R. Master and slave have a 100 Ohm resitor between gnd and common. I'u using a very short wire (30 cm).

Best regards

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