Consider the following sequence (where sent messages include the frame start/end but the response information only shows the within-frame payload without length bytes):
[empty receive buffer]
I start command mode and get the correct ACK
Sending frame: b'\xfd\xfc\xfb\xfa\x04\x00\xff\x00\x01\x00\x04\x03\x02\x01'
Response payload: b'\xff\x01\x00\x00\x03\x00\x80\x00'
Immediately, I send a command 0x0071 but get the wrong ACK
Sending frame: b'\xfd\xfc\xfb\xfa\x0e\x00q\x00\n\x00\x05\x00\x06\x00\x02\x00\x0c\x00\x0b\x00\x04\x03\x02\x01'
Response payload: b'\xff\x01\x00\x00\x03\x00\x80\x00'
So I try again with command 0x0071 and get the correct ACK
Sending frame: b'\xfd\xfc\xfb\xfa\x0e\x00q\x00\n\x00\x05\x00\x06\x00\x02\x00\x0c\x00\x0b\x00\x04\x03\x02\x01'
Response payload: b'q\x01\x00\x00\x00\x00\x00\x00\x0c\x00\x00\x00(\x00\x00\x00(\x00\x00\x00\x05\x00\x00\x00\x05\x00\x00\x00'
This looks like a BUG in the firmware (I have v1.1.1, which is the latest I can see).
Can anyone help avoiding this situation??
For now I just check and retry, but that is not elegant!!
If not, could HLK personnel please refer this to the development team.