Despatch Protocol Plus Modbus Communications - Manual (Page 47)

Chromalox Instruments and Controls
A-51643 Rev. 6 10/06/03 41
Query
Field Name RTU Example Data Description
Header > 3.5 idle characters Start characters
Slave Address $06 Slave number 6
Function $03 Read multiple registers
Starting Address Hi $00 Start reading at holding register 108
Starting Address Lo $6B
No. of Registers Hi $00 Read 3 successive holding registers
No. of Registers Lo $03
CRC Lo $75 CRC = $A075
CRC Hi $A0
Trailer > 3.5 idle characters End characters
Response
Field Name RTU Example Data Description
Header > 3.5 idle characters Start characters
Slave Address $06 Slave number 6
Function $03 Read multiple registers
Byte Count $06 Number of data bytes to follow
Data Hi $02 Contents of holding register 108
Data Lo $2B
Data Hi $00 Contents of holding register 109
Data Lo $00
Data Hi $00 Contents of holding register 110
Data Lo $62
CRC Lo $88 CRC = $8862
CRC Hi $49
Trailer > 3.5 idle characters End characters
6.7.1 The Byte Count Field
When constructing responses in buffers, use a Byte Count value that equals the count of 8-bit bytes in
your message data. The value is exclusive of all other field contents, including the Byte Count field.