CAN Communication
The CAN frame is designed to mimic CANOpen communication protocol.
The CAN ID field is divided into two fields, a 4-bit function code and a 7-bit node ID.
NMT Network Management
The NMT frame is used to configure the operational mode of the motor controller.
To configure the operational mode, the master sends an NMT frame to the slave device. In the NMT frame, byte 0 is set to be the requested mode, and byte 1 is set to be the target device ID.
SDO Service Data Object
The SDO frames are used to configure the device parameters.
To read the current value from a parameter, the master sends out a RECEIVE_SDO frame. The 5-7 bit in byte 0 should be set to 2 (upload). Byte 1-2 should be set to the address of the target parameter.
After sending, the master should listen for a TRANSMIT_SDO frame from the slave device. Byte 0-3 should contain the resulting data.
To write a new value to a parameter, the master sends out a RECEIVE_SDO frame. The 5-7 bit in byte 0 should be set to 1 (download). Byte 1-2 should be set to the address of the target parameter. Byte 4-7 should contain the new value of the parameter. The slave does not transmit a response for write requests.
PDO 1 Process Data Object 1
The PDO1 frame is used to detect if the target device is present on the bus. The frame can also be used for debugging purpose.
The master sends out a RECEIVE_PDO_1 frame.
The slave will respond with a TRANSMIT_PDO_1 frame. The data will echo the received frame.
PDO 2 Process Data Object 2
The PDO2 frame is used for normal control.
The master sends out a RECEIVE_PDO_2 frame. The data field contains the target position and velocity in fp32 format.
The slave will respond with a TRANSMIT_PDO_2 frame. The data field contains the measured position and measured velocity in fp32 format.
PDO 3 Process Data Object 3
The PDO3 frame is used for torque compensation control.
The master sends out a RECEIVE_PDO_3 frame. The data field contains the target position and target feed-forward torque in fp32 format.
The slave will respond with a TRANSMIT_PDO_3 frame. The data field contains the measured position and measured torque in fp32 format.
PDO 4 Process Data Object 4
The PDO4 frame is used for event-driven update frame.
When fast-frame update is enabled, the slave will periodically send out TRANSMIT_PDO_4 frames containing the current measured position and velocity.
FLASH Flash Operation
The FLASH frame is used to save and load the configuration parameters.
When storing the current parameters to flash, the master sends out a FLASH frame. Byte 0 should set to 1 (store).
When loading the current parameters to flash, the master sends out a FLASH frame. Byte 0 should set to 2 (load).
In both cases, the slave will not respond frame.
HEARTBEAT Heartbeat
The HEARTBEAT frame is used to update the safety watchdog timer.
The master sends out a HEARTBEAT frame. Upon receiving the frame, the slave will reset its safety watchdog timer.
Troubleshoot the CAN communication
ip -details -statistics link show canXLog all data and error frames
candump -l any,0:0,#FFFFFFFFExample:
tk@tk-MINI-S:~/Desktop/berkeley_humanoid_lite_lowlevel$ ip -details -statistics link show can2
10: can2: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10
link/can promiscuity 0 minmtu 0 maxmtu 0
can state ERROR-ACTIVE restart-ms 0
bitrate 1000000 sample-point 0.750
tq 62 prop-seg 5 phase-seg1 6 phase-seg2 4 sjw 1
gs_usb: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..1024 brp-inc 1
clock 48000000
re-started bus-errors arbit-lost error-warn error-pass bus-off
0 0 0 0 0 0 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 parentbus usb parentdev 1-3.3:1.0
RX: bytes packets errors dropped missed mcast
0 0 0 0 0 0
TX: bytes packets errors dropped carrier collsns
0 0 0 0 0 0
tk@tk-MINI-S:~/Desktop/berkeley_humanoid_lite_lowlevel$ ip -details -statistics link show can3
11: can3: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10
link/can promiscuity 0 minmtu 0 maxmtu 0
can state ERROR-ACTIVE restart-ms 0
bitrate 1000000 sample-point 0.750
tq 62 prop-seg 5 phase-seg1 6 phase-seg2 4 sjw 1
gs_usb: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..1024 brp-inc 1
clock 48000000
re-started bus-errors arbit-lost error-warn error-pass bus-off
0 0 0 0 0 0 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 parentbus usb parentdev 1-3.4:1.0
RX: bytes packets errors dropped missed mcast
0 0 0 0 0 0
TX: bytes packets errors dropped carrier collsns
0 0 0 0 0 0
Minimizing the CAN noise
Here are some good resources on how to properly do CAN electrical connections:
Decap and common-mode choke: https://community.st.com/t5/stm32-mcus-products/can-bus-massive-noise-on-the-bus-when-a-power-converter-starts/td-p/682045
Split termination: https://electronics.stackexchange.com/questions/512653/can-split-termination-capacitor-calculation
How Termination CAN Improve EMC Performance in a CAN Transceiver: https://www.ti.com/lit/ta/ssztam0/ssztam0.pdf?ts=1750097536718
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