Rockwell Automation 2706-P42_P43_P44_P72_P74_P92_P94 InView Marquee Message Display User Manual - Manual (Page 81)

Publication 2706-UM016D-EN-P - March 2006
InView Protocol 4-15
ASCII Message Frame Format
Beginning of Frame Field
Each transmission will start with a : and is used to signal the receiving
device that message packet follows.
Address Field
Each slave must be assigned a unique address. When a master sends
to a specific slave address (query), the slave sends a response
(response) message back to the master. When a master sends a
message to a specific display address (001 to 247), the slave will give a
response if the message data is correct. All other slaves will ignore the
data transmission.
When a master sends a broadcast message addressed of 255 (0xff),
then all slaves interpret this as an instruction to read and take action
on the message. No response message is required.
Modbus allows 001 through 247 for unique addresses that are used on
a network. The products allow for address 001 through 255, with 255
being the broadcast address. Since some networks may not support
address 248 through 255, then the broadcast address may not be used,
and message queries are always guaranteed. If Modbus message
transmissions are being generated from a serial port, then addressing
from 001 through 255 are valid.
Function Field
The function field tells the address slave what function to perform.
There are only four functions that are applicable to the display
application.
Beginning Of Frame Address Function Data Error Check (LRC) EOF LF
: 2 – char
16 – bits 2 – char
16 – bits N x 4 – char
N x 16 – bits 2 – char
16 – bits 0x0d 0x0a
TIP
When a query/response is used for sending
messages to the display, the display responds back
to the host in less than 10 ms after receiving the Line
Feed field (0x0a).