Dear all,

I have one problem with MAX485 chip. I have correcly connected it to IOT2020 and I use mraa library for write and read data. If I connect the IOT2020 RS485 (by MAX485) to my laptop I correctly see the send data and I can receive the data on IOT. If I connect the IOT RS485 to the final device, I see on it te RX led turn on but it sometimes answer (not correctly) and sometimes no answer.

I think that I have a electrical problems (like a voltage level) on MAX485 connection.

Thanks

Thanks bergmanu but I think that this is not my case.

I use a SUART RS232 connection for drive a MAX232 chip on IOT2020. I have put 120 Ohm terminal resistor at both termination network side.

Massimiliano

Can you provide a connection diagram from MAX485 to the IOT2020 ?

Important is the connection and timing of the send/receive pin of MAX485 (RE/DE).

Ocean_

Can you provide a connection diagram from MAX485 to the IOT2020 ?

Important is the connection and timing of the send/receive pin of MAX485 (RE/DE).

 Ciao Ocean_ I think that the problem is RE/!DE. It driving me nuts!

I use this code for sending and receive the data:

The problem of IOT2020 is that the I/O pins not fast enough for switching of send/receive pin. I suggest a automatic switching of send/receive pin. Look in Google for "MAX485 automatic switch". On the attachment you can see a example MAX485 switch. Good luck. 

Thank you Ocean_

I suppose this problem... In your opinion what is the best eletrical circuit for do this, the previous one with transistor or this in a picture.

Massimiliano

I solved the problem. in fact the outputs are too slow. I have put a transistor on TX signal for enable the DE line and disable RE during transmission.

I hope this can be help.

Massimiliano