Mitsubishi Electric MELSEC iQ-R Series User Manual page 110

Framing error on the target device side
While nothing is being transmitted from C24 to the target device though the RS-422/485 interface, a framing error may be
generated in the target device.
Make the target device skip the data up to transmission of the head data (ENQ, NAK, etc.) of the message from C24.
Before communicating data through the RS-422/485 interface, check the interface specifications on the C24 side.
MELSEC iQ-R Serial Communication Module User's Manual (Startup)
Data bit settings
When adding a sum check code to a message, set "Data bit" to "8".
Navigation window  [Parameter]  [Module Information]  "Module Name"  [Module Parameter]  "Basic Settings"
 "Various control specification"
4 DATA COMMUNICATION USING BIDIRECTIONAL PROTOCOL
108
4.4 Considerations for Data Communication