RS485 with raspberry problems??? Help me pls

[Nguyen Tu]

Hello every one.

I use libmodbus on my raspberry pi with modbus RS485 to create a server. I connected RPi pins with module RS485 (using IC MAX3485) like this:

TX(RPi) <-------->RX(485)

RX(RPi) <-------->TX(485)

GPIO1 <--------> EN485

I set en485 pin to high lvl for transmiting data to a slave on my PC, it work good, but the problem is i cant set en485 pin to low lvl for receiving confirmation from slave! The function

I tried edit src modbus-rtu.c:

if (mode == MODBUS_RTU_RS485) {
            rs485conf.flags = SER_RS485_ENABLED;
            rs485conf.flags |= SER_RS485_RTS_ON_SEND; //Set logical level for RTS pin equal 1 when sending
            rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND); //Set logical level for RTS pin equal 0 after sending
            rs485conf.delay_rts_before_send = 0;
            rs485conf.delay_rts_before_send = 0;

            rs485conf.flags |= SER_RS485_USE_GPIO;
            rs485conf.gpio_pin = en485; // need #define en485 18 //BCM code
            if (ioctl(ctx->s, TIOCSRS485, &rs485conf) < 0) {
                return -1;
            }

but it won't work!
Is any one have idea to solve my problem or sample code, pls send me. Thank you very much.

[Marek Taszek]

hey look at my problem - https://groups.google.com/forum/#!topic/libmodbus/LhHfKgnZU-U

You have raspberry pi and max3485, i have beaglebone black and IL3585.

I use this - https://github.com/stephane/libmodbus/wiki/Beaglebone-RS485-cape but it dosen't work to the end.

First send and receive data is ok but after is CRC Error.

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