Chapter 8 MODBUS Communications8-12 Revision June 2010RTU Mode:Command message: Response message:ADR 01H ADR 01HCMD 06H CMD 06H02H (Upper bytes) 02H (Upper bytes)Starting dataaddress 00H (Lower bytes)Starting dataaddress 00H (Lower bytes)00H (Upper bytes) 00H (Upper bytes)Content of data 64H (Lower bytes) Content of data 64H (Lower bytes)CRC Check Low 89H (Lower bytes) CRC Check Low 89H (Lower bytes)CRC Check High 99H (Upper bytes) CRC Check High 99H (Upper bytes)LRC (ASCII Mode):LRC (Longitudinal Redundancy Check) is calculated by summing up, module 256, the valuesof the bytes from ADR to last data character then calculating the hexadecimal representationof the 2’s-complement negation of the sum.For example, reading 1 word from address 0201H of the ASDA-B2 series AC servo drive withaddress 01H.STX ‘:’‘0’ADR ‘1’‘0’CMD ‘3’‘0’‘2’‘0’Starting data address‘1’‘0’‘0’‘0’Number of data‘1’‘F’LRC Check ‘8’End 1 (0DH)(CR)End 0 (0AH)(LF)01H+03H+02H+01H+00H+01H = 08H, the 2’s complement negation of 08H is F8H.Hence, we can know that LRC CHK is ’F’,’8’.
