Spectrum Controls InView Series User Manual page 76

4-12 Chapter 4: InView Protocol
Beg of
Address
Frame
2-char
:
16-bits
NOTE
User's Manual 0300277-02 Rev. D
ASCII Message Frame Format
Function
2-char
N × 4-char
N × 16-bits
16-bits
Beginning of Frame Field
Each transmission will start with a colon (:) 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 (0×ff), 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.
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
LineFeed field (0×0a).
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.
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.
Error
Data Check
(LRC)
2-char
16-bits
EOF LF
0×0d 0×0a