RO signal unabled

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Giuseppe Giancola

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Mar 26, 2015, 7:06:15 AM3/26/15

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hi, i'm trying libmodbus with raspberry pi b+, i've compiled the 3.1.1 with wiringpi and now i have the rts signal function properly. i have this board with max485 https://www.homegear.eu/images/1/10/RS485_Serial_Module_Wiring.png and have connected with DE,RE signals together. now my problem is that when i start the transmission I have the outpu right output signal, but when i receive i have nothing, as you can see in the image in the attachment. i've replaced the max485 with a texas instruments ic http://www.ti.com/lit/ds/slls877f/slls877f.pdf , thy are pin compatible, but this one is suited for 3.3 applications, but nothing seems to happen.
i use an SDM630 multimeter to talk with modbus, in the idle times it puts on the bus a generic signal at a very high frequency, is it normal?
thanks in advance an sorry for my english. for further infos please ask me.