CAN Bus

The CAN bus signal of NRU-50 is directly from the Jetson Xavier NX module with an additional isolated transceiver. The CAN bus of Jetson Xavier NX is from Bosch Time-Triggered Controller Area Network (M_TTCAN) controller version 3.2.0. It supports CAN 2.0.

System Node

Execute the following script before using the CAN bus on NRU-50. Please double confirm the CAN Bus configuration with other connected CAN devices, especially:

• Bitrate

• Payload bit rate

• Bus error reporting

Initialization Script

modprobe can
modprobe can-raw
modprobe mttcan

sudo ip link set can0 up type can bitrate 500000

If you have initially the CAN bus successfully, you will see can0 in the result of ifconfig, e.g.,

can0: flags=193<UP,RUNNING,NOARP>  mtu 72
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 10  (UNSPEC)
        RX packets 1118  bytes 8944 (8.9 KB)
        RX errors 1117  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 64

Then you can access the CAN Bus on panel via can0

Pin Definition

Pin	Definition
1	GND
2	Reserved
3	CAN_H
4	Reserved
5	CAN_L
6	Reserved
7	Reserved
8	Reserved
9	Reserved

120 Ohm Termination

Make sure you have enabled the 120 Ohm termination of the two ends of your CAN Bus. NRU-50 have an on-board termination which can be controlled via GPIO.

You may enable and disable it by the following commands.

# JetPack 6.x 
# sudo -s
## init CAN Bus Termination Control
function setGPO_JP6(){ 
# $1=gpo_id $2=gpo_value
    PIN=$1
    sudo pkill -f -- "$(sudo gpiofind $PIN)"
    sudo gpioset -m signal $(sudo gpiofind $PIN)=$2 &
}

## Enable CAN Bus Termination
setGPO_JP6 PCC.00 1

## Disable CAN Bus Termination
setGPO_JP6 PCC.00 0


# JetPack 5.x 
# sudo -s
## init CAN Bus Termination Control
CAN_T_NAME=PCC.00
CAN_T_GPIO=328
echo $CAN_T_GPIO > /sys/class/gpio/export
echo out > /sys/class/gpio/$CAN_T_NAME/direction

## Enable CAN Bus Termination
echo 1 > /sys/class/gpio/$CAN_T_NAME/value

## Disable CAN Bus Termination
echo 0 > /sys/class/gpio/$CAN_T_NAME/value



# JetPack 4.x
## Enable CAN Bus Termination
sudo echo 264 > /sys/class/gpio/export # CAN0_TERM
sudo echo out > /sys/class/gpio/gpio264/direction
sudo echo 1 > /sys/class/gpio/gpio264/value

## Disable CAN Bus Termination
sudo echo 264 > /sys/class/gpio/export # CAN0_TERM
sudo echo out > /sys/class/gpio/gpio264/direction
sudo echo 0 > /sys/class/gpio/gpio264/value

Loopback Test

• Initialize CAN bus in loopback mode by the following commands.

modprobe can
modprobe can-raw
modprobe mttcan

# loopback mode
sudo ip link set can0 down
sudo ip link set can0 up type can bitrate 500000 loopback on

• Open a terminal to send random CAN bus data

 cangen can0 -v

• Open another terminal to receive CAN bus data

candump can0 -L

root@nru50-0810:~# candump can0 -L
(1628586540.226617) can0 123#AB123552
(1628586540.226643) can0 123#AB123552
(1628586543.588021) can0 123#AB123555
(1628586543.588052) can0 123#AB123555
(1628586550.445799) can0 123#AB123556
(1628586550.445829) can0 123#AB123556
(1628586555.506052) can0 123#CC222444
(1628586555.506078) can0 123#CC222444

RS232 to CAN Bus Test via UT-2505

One of the common tools to test RS-232 to CAN Bus communication is UT-2505 from CONSTEEL Electronics. A quick memo for testing is as follows.

0. Prerequisites

• Please remember to install minicom for further COM port testing.

sudo apt update
sudo apt install -y minicom

• Then, disable debug UART for one time and initialize the CAN bus after every reboot.

• Please make sure you have hardware configured COM port as RS-232 mode.

1. Test RS232 to CAN

Open two terminals: one for receiving CAN data, one for sending data via RS232.

Receiving Terminal

Type the following command to open candump to show any incoming CAN bus data.

candump can0 -L

Sending Terminal

Type the following command to open minicom to send data via COM.

sudo minicom -D /dev/ttyTHS0 -b 9600 -H -w

Type any characters in minicom, and you will see the result in receiving terminal, e.g.,

root@nru50-0813-1058:~# candump can0 -L
(1628824824.623881) can0 07FFFFFF#41
(1628824824.917790) can0 07FFFFFF#7A
(1628824825.991474) can0 07FFFFFF#73
(1628824827.880887) can0 07FFFFFF#73
(1628824827.983239) can0 07FFFFFF#64
(1628824828.055279) can0 07FFFFFF#61
(1628824828.130766) can0 07FFFFFF#73

2. Test CAN to RS232

Open two terminals: one for sending CAN data, one for receiving data via RS-232.

Receiving Terminal

Type the following command to open minicom to show any incoming data via RS-232.

sudo minicom -D /dev/ttyTHS0 -b 9600 -H -w

Sending Terminal

Type the following command to use cangen to generate random CAN bus data.

cangen can0 -v

Then you will see random generated CAN data shown in minicom, e.g.,

Welcome to minicom 2.7.1

OPTIONS: I18n
Compiled on Aug 13 2017, 15:25:34.
Port /dev/ttyTHS0, 11:20:32

Press CTRL-A Z for help on special keys

00 00 02 36 30 d2 b5 08 3a 23 9b 31 00 00 01 45 38 39 94 5f 06 29 c7 14 00 00 00 54 00 00 05 fa 18 da 0b 38 4f 48 68 2b 00 00 01 54 89 1e c8 28 12 e0 c9 00 00 00 79 92 f5 1
4 1b 2f 00 00 05 ac 87 55 54 12 cf 06 10 52 00 00 07 e5 c6 91 00 00 03 2e 55 15 22 55 73 6c 8d 00 00 01 c2 7a 95 54 7f 16 12 d8 36 00 00 03 be 4b 45 11 3f b8 00 00 05 41 07
 c2 43 00 00 04 5b 00 00 06 45 03 c4 3f 07 f2 13 9d 77 00 00 07 c7 c1 1a ad 49 ac 7f ef 1e 00 00 00 ed c7 71 76 42 1b 8c 55 00 00 00 7e 8f f8 e2 35 41 8a 2f 09 00 00 05 aa
57 9c 07 40 68 e9 af 39 00 00 03 2e 20 63 00 00 01 06 06 5f ba 13 61 bd 80 00 00 05 b8 35 02 9b 64 fd a3 07 58 00 00 01 e8 ef b7 a4 4f af 59 db 52 00 00 07 c4 00 00 07 38 c
d 0c 00 00 02 3f f7 19 b7 19 ea a7 28 18 00 00 03 65 52 91 d8 51 93 a6 8c 54 00 00 07 f1 03 a7 dc 00 00 01 9a 58 56 8e 0