Wondering if anyone can give us some advice on what this error message means (and how we can figure it out on our own in the future)?
We are getting it on a MangoES.
It means the modbus slave responded with an error packet, but googling reveals there is no exception code 0x80!
This likely means that your serial bus isn't configured correctly (and the CRC error supports that). I would guess your parity setting doesn't match the parity setting of the device, but you should double check the buad rate, data bits, stop bits, etc. against the manual for the device.