ProSoft Technology MVI69L-MBTCP - Manual (Page 124)

Reference MVI69L-MBTCP ♦ CompactLogix Platform
User Manual Communication Module
Page 124 of 152 ProSoft Technology, Inc.
January 6, 2014
Addr in Dev - same as when Float Flag: Y as long as the Server's Float Flag =
Y.
In the above example, the Client's Modbus command to transmit inside the
Modbus packet will be as follows.
Server
address Function
Code Address in
Device Reg
Count Byte
Count Data
DEC 01 16 7100 2 4 85.37
HEX 01 10 1B BC 00 02 04 BD 71 42 AA
In this example, the Client's Modbus packet contains the data byte and data word
counts that have NOT been doubled from the amount specified by Reg Count
due to the Float Flag set to N. The Server looks for the byte count in the data
packet to know the length of the data to read from the wire. Because of
insufficient byte count, some servers will read only half the data from the Client's
transmission. Other servers will read all 8 bytes in this example because they will
know where in the packet the data starts and ignore the byte count parameter
inside the Modbus packet.
Specific Example#3: Client is issuing Modbus command with FC 3 to transfer Float data
from Server.
Float Flag: Not applicable with Modbus Function Code 3.
Float Start: Not applicable with Modbus Function Code 3.
DB Addr - Tells the Client where in its data memory to store the data obtained
from the Server.
Reg Count - Tells the Client how many registers to request from the Server.
Swap Code - same as above.