Short problem description:
I'm trying to get my RS485 cape to work on a BeagleBone running Debian. I
can't receive any response from the slave device though sending works OK.
Longer description:
I am accessing my BB using SSH over Ethernet (not ttyO0). My BB is booting
from microSD with Debian (3.8.13-bone30 from armhf.com).
I have loaded BB-BONE-UART4 to the cape manager - all OK. I configure the
/dev/ttyO4 for 115200 / 8n1 using stty (confirmed correct settings for my
slave device), and I can send traffic by echo'ing to /dev/ttyO4. At the
other end of the RS485 line the slave device receives the command OK (I can
toggle its LED).
But the BeagleBone only shows the local echo of the sent traffic, *never
any response from the slave*. After the local echo I only see a
never-ending stream of junk characters repeating. To view the response, I
use the following script in a separate terminal:
stty -F /dev/${device} raw
stty -F /dev/${device} 115200
cat /dev/${device} |hexdump -C
I have also tried with
stty -F /dev/${device} 115200 cs8 -cstopb -parenb -brkint -icrnl -imaxbel
-opost
tail -c +1 -f /dev/ttyO4 | hexdump -C
but it makes no difference to the output.
I have tested the slave with a PC and RS485-to-USB cable, and it works
perfectly at 115200 / 8n1.
I have tested the cape on a BeagleBoneBlack (disabling HDMI and eMMC
virtual capes) and I get the same problem.
I have even seen the same symptoms when testing the slave + a completely
different cape (which also has an on-board RS-485 controller and its own
overlay, which is loaded OK).
I have tested using different power supplies for slave and BB (joint and
separate supply).
I tested using a clean install of Debian.
I have tested with other UARTs (ttyO2, ttyO5) - same result.
Things I have NOT yet done:
1) tested with Angstrom Linux (standard with BB and BBB)
2) terminated the RS-485 line endpoints with resistors (the line is 15-30
cm ... should not be necessary).
3) tested at lower baud rate
Basically I am out of feasible ideas ...
Can anyone suggest anything else I can investigate or check?
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