RS485 Raw Passthrough

Raw RS485 passthrough sends device data received from USB directly onto the RS485 bus and returns device feedback unchanged. It does not add a channel number or SANPO wrapper.

For continuous high-rate real-time control, use the wrapped SANPO USB to RS485 protocol.

USB Serial Ports and RS485 Interfaces

A complete board normally exposes two USB serial ports. One controls RS485-1 and RS485-2, and the other controls RS485-3 and RS485-4.

Windows shows two COM ports, while Linux normally shows two /dev/ttyACM* devices. Operating-system numbering may not follow the board interface order. For first use, connect only one RS485 device and send a test command to identify the correct port.

Raw data sent to one USB serial port is transmitted on both RS485 channels in that group. To select only one of RS485-1/2/3/4, use the wrapped SANPO USB to RS485 protocol.

Procedure

  1. Connect the board to the PC through USB.

  2. Connect and power the RS485 motor or device.

  3. Open the corresponding COM or /dev/ttyACM* port.

  4. Match the device bitrate, stop bits, parity, and data bits.

  5. Send one complete device command as binary data.

  6. If the device replies, the host receives its binary feedback.

The serial settings selected when opening the USB port are also used by the two RS485 channels in that group. Factory defaults are 4 Mbps, one stop bit, no parity, and eight data bits.

Save Default RS485 Settings

To use specific settings after power-up, send the following through the current USB serial port:

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

Parameter

Values

Bitrate

1200 to 4000000

Stop bits

1 or 2

Parity

0: none; 1: odd; 2: even

Data bits

8 or 9

Example for 4 Mbps, one stop bit, no parity, and eight data bits:

AT+SETRS485=4000000,1,0,8\r\n

Send the command as text with a CRLF line ending. Success returns:

OK\r\n

The setting is saved across power cycles. Opening the USB port later applies the settings selected by the host again, so keep the host and saved settings consistent.

Unitree GO-M8010 Test

  1. Configure the motor communication settings in the host application.

  2. Select binary or hexadecimal transmission.

  3. Send:

FE EE 11 00 00 00 00 00 00 00 00 00 00 00 00 18 7C

If the motor ID, settings, wiring, and power are correct, the host receives binary motor feedback. Decode it according to the motor manufacturer’s protocol.

Limitations

  • Do not send more than 72 bytes at once. Prefer one complete device command per transmission.

  • Both RS485 channels associated with the USB port receive the command. Use different device IDs and avoid simultaneous replies when sharing the port.

  • Device commands must not begin with 41 54, 45 54, or 53 54. Contact support if the device protocol uses one of these prefixes.

Troubleshooting

Symptom

Action

No USB serial port

Check the USB cable, connector, and driver, then reconnect the board

Unsure which two RS485 channels a port controls

Connect one device and test both USB serial ports

USB port is busy

Close other software using the port and reopen it

No reply

Check device power, A/B wiring, device ID, checksum, and serial settings

Corrupted data or wrong length

Match bitrate, stop bits, parity, and data bits, and inspect A/B signal quality

Both RS485 channels receive the command

This is expected in raw mode; use the wrapped SANPO USB to RS485 protocol to select one channel