ProSoft Technology MVI69L-MBS - Manual (Page 120)

Reference MVI69L-MBS ♦ CompactLogix Platform
User Manual Communication Module
Page 120 of 154 ProSoft Technology, Inc.
January 6, 2014
Addr in Dev - Tells the Master where in the Slave's database to locate the data.
In the above example, the Master's Modbus command to transmit inside the
Modbus packet is as follows.
Slave
address
Function
Code
Address in
Device
Reg count Byte Count Data
DEC 01 16 7100 2 8 85.37 22.86
HEX 01 10 1B BC 00 02 08 BD 71 42 AA E1 48 41 B6
In this example, the Master's Modbus packet contains the data byte and data
word counts that have been doubled from the amount specified by Reg Count
due to the Float flag set to Y. Some Slaves look for the byte count in the data
packet to know the length of the data to read from the wire. Other slaves know at
which byte the data begins and read from the wire the remaining bytes in the
packet as the data the Master is sending.
Specific Example#2: Master is issuing Modbus command with FC 16 (with Float Flag: No) to
transfer Float data.
Float Flag: "N" tells the Master to ignore the floating values and treat each
register data as a data point composed of 1 word, 2 bytes or 16 bits.
Float Start: Ignored.
DB Addr - same as when Float Flag: Y.
Reg Count - Tells the Master how many data points to send to the Slave.
Swap Code - same as when Float Flag: Y.
Func Code - same as when Float Flag: Y.