K-Patents SeedMaster 2 - Manual (Page 80)

11 COMMUNICATION 80
80
Response:
A F RAH RAL RNH RNL
Notation:
A SeedMaster 2 address (station address)
F command code
RAH, RAL base address of MODBUS registers,
RAH: high, RAL: low address byte
RNH, RNL number of MODBUS registers,
RNH: high, RNL: low byte of the number
BN number of data bytes sent (0…255)
D1…Dn data bytes, n=number of registers*2,
high byte first
Length of a MODBUS register: 2 bytes
The MODBUS /TCP messages consist of 3 parts:
• Header (7 bytes)
• Command code (1 byte)
• Data bytes
Header structure:
Field name Length Description Client Server
Transaction ID 2 bytes MODBUS Set by the Copies the ID
transaction Client set by the Client
identity in the response
Protocol ID 2 bytes 0 = MODBUS Set by the Copies the ID
Client
set by the Client
in the response
Length 2 bytes Number of the Set by the Set by the
bytes which Client Server
follow (Request) (Response)
Device ID 1 byte Identity of the Set by the Copies the ID
serial line, or Client set by the Client
Ethernet device in the response
Transmission example:
The numbers shown are hexadecimal without spaces (the spaces inserted below are only to make reading
easier).
Client’s request to READ REGISTERS:
25 00 00 00 00 06 15 03 00 00 00 0C
complete message
25 00 00 00 00 06 15 header, SeedMaster 2 ID = 15(hex) = 21 (decimal)
03 command code (READ)
00 00 register base address
00 0C number of registers = 0C (hex) = 12 (decimal)
6 bytes
SeedMaster 2 response:
25 00 00 00 00 1B 15 03 18 6B 85 42 9D 85 1F 42 8B 97 ED 44 B7 6E CC 42 AC 00 00 00 00 00 00 00 00