The BeagleBone's omap-serial driver doesn't support RS-485 DE/RE control with the RTS flow control signal. Instead it has an RS-485 mode using a GPIO pin for DE/RE control, and has a modified serial_rs485 struct from the standard serial driver. You have to use ioctl on the corresponding /dev/ttyOx file to put the serial driver in RS-485 mode and tell it which pin to use, and you also have to take care of muxing the pin to GPIO mode.
So with the jumper in the RTS position that would be the GPIO signal that shares the pin with the UART4 RTS signal, so that's GPIO0_9 on P8.33. Or you can put it to the GPIO1_16 position and use GPIO1_16 instead. (I believe GPIO1_16 There's a tutorial here: http://inspire.logicsupply.com/2014/09/beaglebone-rs-485-communication.html Also, I believe RS485B is the inverting output, so you have your +/- swapped. On Wednesday, August 26, 2015 at 2:41:49 PM UTC-4, benjamin...@gmail.com wrote: > > Hello, > > I have a BeagleBone Black with a "Serial Cape" ( > http://www.logicsupply.com/eu-en/cbb-serial/). This cape supports RS-485 > which i'm interested in. Before i had this cape, i used a > RS-485-to-USB-converter. > > > My problem: > I try to read some data from an external device. It's very simple: The > request is just "/?!\r\n" and then i get the data. > > With the RS485-to-USB-Stick i used this serial port configuration (with > ser2net): > /dev/ttyUSB0 9600 7DATABITS EVEN 1STOPBIT > > With the cape i tried this configuration: > /dev/ttyO4 9600 7DATABITS EVEN 1STOPBIT > > Unfortunately this first try didn't work. I didn't get any response. I > also tried this configuration: > /dev/ttyO4 9600 7DATABITS EVEN 1STOPBIT RTSCTS > > I set the jumpers on the cape like this: > J8: RS485 > J7: UART4 RTS > > The RS485+ wire is connected to the RS485B port, and the RS485- wire is > connected to the RS485A port. > ( > https://docs.google.com/document/d/1sgurQ-7gLyn7g-Kg983NRM0aDkYEqHqy9dmrieX_RUM/edit > > page7) > > To get a better overview i made a photo: > > > <https://lh3.googleusercontent.com/-DGOBBHIo6sM/Vd1xuVsgc_I/AAAAAAAAAEE/JS4oAhPYoOk/s1600/IMG_20150826_091607_mod.jpg> > > > At the bottom of the picture there is the RS485-to-USB converter. It just > has two ports which i used to connect the RS485 wires. > > I think the board itself should work, because if i execute "cat > /sys/devices/bone_capemgr.*/slots" i can see it. > > My question: > Do i do something wrong? Maybe someone else has used this cape with RS485? > I thought it should be almost as easy as with the USB converter? > > > Thank you for any help > > Best regards > Benj > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
