Communication Settings

V6 USB serial and SPI protocols use CAN, CAN FD, and RS485 settings stored by the firmware. Linux SocketCAN uses settings configured by Linux. These are separate configuration paths.

Host method	Where to configure	After a power cycle
USB serial / SPI	Send `AT+` commands through USB serial	Saved settings remain active
SocketCAN	Linux `ip link`	Configure each `canX` interface again

Send AT+ commands as text with a CRLF line ending. Do not send the characters \r\n as ordinary text.

Factory Defaults

Item	Default
Classic CAN	1 Mbps
CAN FD arbitration phase	1 Mbps
CAN FD data phase	5 Mbps
RS485	4 Mbps, one stop bit, no parity, eight data bits
SPI	SHORT, 23 bytes
RS485 RAW replies	Disabled
RS485 RAW target	`0`, both RS485 channels on the current MCU

Configure CAN and CAN FD

AT+SETFDCAN=<arbitration-bitrate>,<data-bitrate>

The first parameter is used for classic CAN and the CAN FD arbitration phase. The second parameter is used only for the CAN FD data phase.

Parameter	Supported values
Arbitration phase	`1000000`, `500000`, `250000`, `125000`, `100000`
Data phase	`2000000`, `3000000`, `4000000`, `5000000`

All four CAN FD data rates use exact bit timing with 0% frequency error. Prefer the device’s factory default, normally 5 Mbps, and change it only when every device on the bus uses the same setting.

Set classic CAN/CAN FD arbitration to 1 Mbps and CAN FD data to 5 Mbps:

AT+SETFDCAN=1000000,5000000

Success returns:

OK

Query the current values:

AT+SETFDCAN?

Example response:

FDCAN:1000000,5000000

The setting is applied to both CAN/CAN FD interfaces on the current MCU and saved to Flash.

Configure RS485

AT+SETRS485=<bitrate>,<stop-bits>,<parity>,<data-bits>

Parameter	Supported values
Bitrate	`1200` to `4000000`
Stop bits	`1` or `2`
Parity	`0`: none; `1`: odd; `2`: even
Data bits	`8` or `9`

Example for Unitree’s common 4 Mbps, 8-N-1 setting:

AT+SETRS485=4000000,1,0,8

Query the current value:

AT+SETRS485?

Example response:

RS485:4000000,1,0,8

The setting is applied to both RS485 interfaces on the current MCU and saved to Flash.

Configure SPI Length

AT+SPIMODE?
AT+SPIMODE=SHORT
AT+SPIMODE=LONG

Mode	SPI transfer	Purpose
SHORT	23 bytes	Classic CAN; up to 18 bytes of RS485 data
LONG	73 bytes	Classic CAN, CAN FD; up to 68 bytes of RS485 data

Success returns OK, and the setting is saved. The SPI host must stop current transfers, wait at least 10 ms, and then use the new fixed length.

SocketCAN Settings

Linux configures SocketCAN. Classic CAN example:

sudo ip link set can0 down
sudo ip link set can0 type can bitrate 1000000
sudo ip link set can0 up

CAN FD example:

sudo ip link set can0 down
sudo ip link set can0 type can bitrate 1000000 dbitrate 5000000 fd on
sudo ip link set can0 up

Check the result:

ip -details link show can0

SocketCAN, USB serial, and SPI ultimately use the same physical CAN controller. If several host paths reconfigure the same interface, the last setting becomes active. In production, use one host entry point to control a given CAN bus.

Restore Communication Defaults

AT+CFGERASE

Success returns OK and restores the defaults on this page. The command clears saved CAN/CAN FD, RS485, SPI mode, RAW target, and power-on batch settings. It does not delete offline batch contents or factory identification.

If repeated configuration changes return ERR,5, use this command to clear the communication configuration area and then set the required values again.

Troubleshooting

Symptom	Action
Changing the USB terminal bitrate does not change the bus speed	This is normal for a virtual USB serial port; use the `AT+` commands on this page
A configuration command returns nothing	Send it as text with a `CRLF` line ending
Command returns `ERR,1` or `ERR,3`	Check the parameter count and allowed values
Command returns `ERR,5`	The configuration area is full; run `AT+CFGERASE` and configure it again
SocketCAN stops working after reconnecting	Reapply the Linux `ip link` configuration