Hi Craig Markwardt Thanks for your reply. I search some of this kind of article, and it seems doesn't easy to understand the architecture. Like this link: http://passive-components.eu/understanding-rs-485-passive-fail-safe-biasing/ Do you have any use case for me to reference? It will be very useful for me to design on our board.
Thanks a lot, Harvey Craig Markwardt於 2016年12月14日星期三 UTC+8上午12時33分03秒寫道： > > > Greetings--- I have experienced this problem before. It is likely an > issue with the physical interface, not software. Basically the issue is > that the receiver is still receiving when the line goes to an idle > undefined state, and receives "garbage" data. Search for RS 485 failsafe > bias for more background. You will need some kind of biasing resistor to > pull the line(s) up to a true idle state. > > > On Monday, December 12, 2016 at 11:15:17 PM UTC-5, 張皓傑 wrote: >> >> Hi all >> >> I'm useing debian 7.11(kernel 3.8) version image. >> I'm trying to use rs485 cape on BBB or BBG. Below are the cape I use. >> 485 CAN CAPE >> http://www.waveshare.com/wiki/RS485_CAN_CAPE >> 485 CLICK BOARD >> http://www.mikroe.com/click/rs485-3.3v/ >> >> As I know these boards don't have capability to auto handle read/write >> mode switching. >> I try to use linux rs485 mode to auto handle switching problem. >> The attached file is my sample code. >> >> My problem is if I read data after writing, the receiving data will add a >> redundant data(0x00) at the beginning of the buffer. >> Below is the result. >> This is modbus command, that due to the redundant data, the modbus >> command will be failed. >> So I use raw command to get data. >> >> send: 01 04 00 00 00 01 31 CA >> receive: 00 01 04 02 01 3E 39 70 >> >> send: 01 04 00 01 00 01 60 0A >> receive: 00 01 04 02 00 E2 39 79 >> >> send: 02 04 00 00 00 01 31 F9 >> receive: 00 02 04 02 00 BA 7C 83 >> >> send: 02 04 00 01 00 01 60 39 >> receive: 00 02 04 02 00 FA 7D 73 >> >> send: 03 04 00 00 00 01 30 28 >> receive: 00 03 04 02 03 11 00 0C >> >> send: 03 04 00 01 00 01 61 E8 >> receive: 00 03 04 02 00 DE 40 A8 >> >> This redundant data is not read data from modbus device. I use another >> rs485 cable to monitor the data will not have this redundant data. >> Like this: >> send: 01 04 00 00 00 01 31 CA >> receive: 01 04 02 01 3E 39 70 >> >> If I only use receive mode, there will not be any redundant data in the >> buffer. >> >> As I tried, kernel 4.4 cannot work 485 system call. >> >> I'm not familiar in kernel, does anyone could give me some advice? >> >> Many thanks, >> Harvey >> > -- 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/53ecf4bb-14a6-4737-816b-2a128592e3b3%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
