Rockwell Automation 2706-P42_P43_P44_P72_P74_P92_P94 InView Marquee Message Display User Manual - Manual (Page 82)

Publication 2706-UM016D-EN-P - March 2006
4-16 InView Protocol
Data Field
The data field contains information on the specific action that the
slave must perform.
Error Check Field
The error checking is the LRC of the message and allows for the
master and slave to detect message errors. A response message is only
sent, if the original message was received correctly.
The following shows a simulated query and response.
Simulated Query and Response
End Of File Field
This field is used to signify the end of file for the transmission. It uses
a Carriage Return (0x0d).
Line Feed Field
This is the ready to respond field file (LF) and uses a line feed (0x0a).
Longitudinal Redundancy Check (LRC) Error Detection and
Calculation
Some sort of error detection is needed, because communication errors
can occur in an industrial environment due to machinery noise and
electromagnetic interference. The method for error detection used
with Modbus ASCII is Longitudinal Redundancy Check (LRC). The LRC
is an 8-bit binary number represented and transmitted as two ASCII
Hexadecimal characters. The LRC is produced by adding the message
characters (ignoring the carry bit) and taking the two's compliment of