Skip to content

UART.md

Latest commit

 

History

History
127 lines (87 loc) · 3.5 KB

UART.md

File metadata and controls

127 lines (87 loc) · 3.5 KB

#UART configuration for XBee

###Goal: to connect the Xbee radio to the UART of the beagle.

There are four serial ports on the beagle bone expansion headers. UART ports 1, 2, 4 ports have TX, Rx, RTS and CTS signals while UART5 only has TX and RX. UART 3 is NOT available for use.

I chose to use UART4 because the pins were in a nice location.

##Wiring

I soldered the XBee header pins to the Xbee breakout board and the break out board to the beagle proto cape.

Beagle with Xbee

I wired pin 11 of the P9 expansion header on the beagle (UART4 RX) to DOUT on the Xbee breakout board.

I wired pin 13 of the P9 expansion header on the beagle (UART4 TX) to DIN on the Xbee breakout board.

Software

The beagle multiplexes its pins, so you need to tell it how you're using them.

UART - PinFilesystem locationValue (hex)Notes
UART1 - RX/sys/kernel/debug/omap_mux/uart1_rxd20 Mode 0 - Input
UART1 - TX/sys/kernel/debug/omap_mux/uart1_txd0 Mode 0 - Output
UART2 - RX/sys/kernel/debug/omap_mux/spi0_sclk1 Mode 1 - Input
UART2 - TX/sys/kernel/debug/omap_mux/spi0_d021 Mode 1 - Output
UART4 - RX/sys/kernel/debug/omap_mux/gpmc_wait026 Mode 6 - Input
UART4 - TX/sys/kernel/debug/omap_mux/gpmc_wpn6 Mode 6 - Output
UART5 - RX/sys/kernel/debug/omap_mux/lcd_data924 Mode 4 - Input
UART5 - TX/sys/kernel/debug/omap_mux/lcd_data84 Mode 4 - Output

You can check the configuration:

cat /sys/kernel/debug/omap_mux/gpmc_wait0
cat /sys/kernel/debug/omap_mux/gpmc_wpn

For our case (UART4), we do:

echo 26 > /sys/kernel/debug/omap_mux/gpmc_wait0
echo 6 > /sys/kernel/debug/omap_mux/gpmc_wpn

Now, /dev/ttyO4 (that is a captial letter o) is ready to be used as you would any normal serial port under Linux.

For a sanity test you can just talk directly to the XBee by putting it in configuration mode. Just send '+++' (with no CR or LF) and wait for it to respond 'OK'. If that works, the the hardware is setup correctly.

Note that from the factory, the XBees are configured for 9600 baud, if you change it to a different baud rate it will remember the change. You'll have to communicate at the new baud rate next time.

Here is how to do the whole thing in python:

#!/usr/bin/python

import subprocess
import serial
import time

UART4_RX_conf = "/sys/kernel/debug/omap_mux/gpmc_wait0"
UART4_TX_conf = "/sys/kernel/debug/omap_mux/gpmc_wpn" 

UART4_RX_val = 26
UART4_TX_val = 6

subprocess.call(['echo', str(UART4_RX_val), '>', UART4_RX_conf])
subprocess.call(['echo', str(UART4_TX_val), '>', UART4_TX_conf])

print "echo 'UART 4 (TX):'"
subprocess.call(['cat', UART4_TX_conf])
print ""

print 'echo "UART 4 (RX):"'
subprocess.call(['cat', UART4_RX_conf])
print ""

# open serial port
ser = serial.Serial('/dev/ttyO4')
ser.baudrate = 9600

# go into configure mode
ser.write('+++')
time.sleep(1)
print ser.read() # should see 'O'
print ser.read() # should see 'K'

##Other resources:

BeagleBone serial ports and Xbees