Hey all, I did some further tests. Actually none of the screens from my scope looks like I would expect it...
Picture 1 shows the result, if I try to read something on the bus with a 14s timeout (nothing was sended on the bus...) Pic1 <http://www.ep1.rub.de/~florian/rs485_test_reading_timeout.png> Picture 2 shows the same, but this time there were messages send over the bus. After 49 bytes, the beagle bone toggles the DE/!RE gpio to high for unknown reasons (the test program is still reading from the UART interface) Pic2 <http://www.ep1.rub.de/~florian/rs485_test_reading.png> Picture 3 shows the test, where the BeagleBone is sending Pic3 <http://www.ep1.rub.de/~florian/rs485_test_sending.png> and finally picture 4 shows a test, where the BeagleBone should read (timeout 3s) on the bus, then send something and again reading (with 3s timeout)... Pic4 <http://www.ep1.rub.de/~florian/rs485_test_3sRead-send-3sRead.png> As you see, DE/!RS stays high after sending, although it should be low... In addition I would expect this line to be low when the port is not used, but it's high.. I checked if there is any other process (or driver) accessing GPIO3_19 but I could not find any... Any help is very much appreciated! Florian Am Freitag, 22. April 2016 15:22:48 UTC+2 schrieb [email protected]: > > Hey all, > > I'm using the Debian Jessie image with kernel version 4.4.6-ti-r15 on my > BeagleBone Black. > > To monitor our vacuum system in the lab, we need a RS485 interface, so I > simply connected an ADM2682 RS422/485 line driver > to UART4 of the BeagleBone using this Device Tree Overlay > BB-UART4-RS485-00A0.dts > <https://github.com/RobertCNelson/bb.org-overlays/blob/master/src/arm/BB-UART4-RS485-00A0.dts> > (commit > 16f76f7 on master branch) > > P9.27 is connected to the DE and !RE inputs of the chip. > > Using this for sending works just fine, but I have problems receiving > messages over the bus. > > For testing I wrote a small C-program which should read on the bus until > it gets two times a timeout. > The reading is done via select-call with a 5 second timeout. > The device on the other end of the bus is contentiously sending data over > the bus. > After receiving 49 bytes at most, the DE/!RE line goes up and my > BeagleBone stops receiving any data... > > I've uploaded a screenshot of the scope showing the three signals from the > UART interface > Scope <http://www.ep1.rub.de/~florian/rs485.png> > > Does anyone has a clue what could go wrong? > > Any help appreciated! > Regards > Florian > > > -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/4811b6af-b1dc-4909-a972-62f2c5f35fd2%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
