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Chapter 5 - MODBUS-RTU Communication
77
5.6 Communication Protocol (CMC-BUS ASCII)
The communication structure is that the ACtionMaster drives are slaves and a computer/host is the
master.
5.6.1 Basic Format
Command Message (Request)
ENQ Drive No. CMD Data SUM EOT
1 byte 2 bytes 1 byte n bytes 2 bytes 1 byte
Normal Response (Acknowledge Response)
ACK Drive No. CMD Data SUM EOT
1 byte 2 bytes 1 byte n * 4 bytes 2 bytes 1 byte
Error Response (Negative Acknowledge Response)
NAK Drive No. CMD Error Code SUM EOT
1 byte 2 bytes 1 byte 2 bytes 2 bytes 1 byte
5.6.2 Description:
Request starts with ‘ENQ’ and ends with ‘EOT’.
Acknowledge Response starts with ‘ACK’ and ends with ‘EOT’.
Negative Acknowledge Response starts with ‘NAK’ and ends with ‘EOT’.
‘Drive No.’ is the number of drives set in ‘I/O 48’. The Drive No. is two bytes of ASCII-HEX.
(ASCII-HEX: hexadecimal consists of ‘0’ ~ ‘9’, ‘A’ ~ ‘F’)
‘CMD’: Character letter
Character ASCII-HEX Command
‘R’ 52h Read
‘W’ 57h Write
‘X’ 58h Request for monitoring
‘Y’ 59h Action for monitoring
‘Data’: ASCII-HEX (Ex. When the data value is 3000 : 3000 → ‘0’’B’’B’’8’h → 30h 42h 43h 38h
‘Error Code’: ASCII (20h ~ 7Fh)
Receive/send buffer size: Send = 39 byte, Receive=44 byte
Monitor registration buffer: 8 Word
‘SUM’: to check the communication error.
SUM= ASCII-HEX format of lower 8 bit of (Drive NO. + CMD + DATA)