Operating instructions

Modifying the Configuration File PTQ-MCM ♦ Quantum / Unity Platform
Modbus Communication Module
ProSoft Technology, Inc. Page 73 of 139
April 29, 2008
(Float specific module parameters)
Float Flag: "Y" tells the Master to consider the data values that need to be sent
to the Slave as floating point data where each data value is composed of 2 words
(4 bytes or 32 bits).
Float Start: Tells the Master that if this address number is <= the address
number in "Addr in Dev" parameter to double the byte count quantity to be
included in the Command FC6 or FC16 to be issued to the Slave. Otherwise the
Master will ignore the "Float Flag: Y" and treat data as composed of 1 word, 2
bytes.
(Modbus Command parameters)
DB Addr - Tells the Master where in its data memory is the beginning of data to
obtain and write out to the Slave (slave) device.
Reg Count - Tells the Master how many data points to send to the Slave. Two
counts will mean two floating points with Float Flag: Y and the "Addr in Dev" =>
the "Float Start" Parameter.
Swap Code - Tells the Master how to orient the Byte and Word structure of the
data value. This is device dependent. Check Command Entry formats Section.
Func Code - Tells the Master to write the float values to the Slave. FC16.
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 will be 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 conclusion
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.