Hi Peilang I've had some of the same questions, and based on previous postings on this list RS485 isn't enabled in the regular build - though I understand it is being integrated into the 4.4 release. The issue being the serial port is so overloaded with historical functionality. For RS485 there is a separate \KERNEL\drivers\tty\serial\omap-serial.c
I rebuilt the kernel using RobertCNelson's yakbuild (amazing..) to enable the RS485 capability. The details of what I did are at https://github.com/neilh10/yakbuild/wiki/BBB-RS485-Tutorial I've got messages flowing out where P9.22 is the DirectionEnable <https://lh3.googleusercontent.com/-R6m3a30DVI8/WbFyJ_RPOlI/AAAAAAAASYE/vZelEWSxkpwFl-zUSrzmjadq-7iF8VhuwCLcBGAs/s1600/SalaeLogicRS485direction.JPG> I am building some hardware, and planning on using a MAX13487EESA+ which auto manages the Tx output driver. On Wednesday, June 28, 2017 at 6:33:19 AM UTC-7, [email protected] wrote: > > hi > > The BBB has a kernel 4.4 and has a overlay 'universaln' loaded by default. > I can see there is ttyO[0-4] unuder /dev/. Then I did 'sudo config-pin > P9.13 uart && sudo config-pin P9.11 uart ' and the uart function works > well. > > I wonder how do I enable the RS485 ? I only see there is a overlay > 'BB-UART4-RS485' but when I tried to load it, it said 'file exist'. I read > at the source dtbo and there is a pin P9.27, what is that? > > I want to connect to a device which has rx, tx and gnd, using MODBUS > (half-duplex). > > Thanks > /Peilang > -- 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/5aee2142-c123-43e6-9ca8-673906c36796%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
