Campbell Scientific CR3000 Micrologger - Manual (Page 375)

Section 8. Operation
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8.6.2.3.3 Addressing (ModbusAddr)
Modbus devices have a unique address in each network. Addresses range from 1
to 247. Address 0 is reserved for universal broadcasts. When using the NL100,
use the same number as the Modbus and PakBus® address.
8.6.2.3.4 Supported Function Codes (Function)
Modbus protocol has many function codes. CR3000 commands support the
following.
Table 93. Supported Modbus Function Codes
Code Name Description
01 Read coil/port status Reads the on/off status of discrete output(s) in the ModBusSlave
02 Read input status Reads the on/off status of discrete input(s) in the ModBusSlave
03 Read holding registers Reads the binary contents of holding register(s) in the ModBusSlave
04 Read input registers Reads the binary contents of input register(s) in the ModBusSlave
05 Force single coil/port Forces a single coil/port in the ModBusSlave to either on or off
06 Write single register Writes a value into a holding register in the ModBusSlave
15 Force multiple coils/ports Forces multiple coils/ports in the ModBusSlave to either on or off
16 Write multiple registers Writes values into a series of holding registers in the ModBusSlave
8.6.2.3.5 Reading Inverse-Format Registers
Some Modbus devices require reverse byte order words (CDAB vs. ABCD). This
can be true for either floating point, or integer formats. Since a slave CR3000
uses the ABCD format, either the master has to make an adjustment, which is
sometimes possible, or the CR3000 needs to output reverse-byte order words. To
reverse the byte order in the CR3000, use the MoveBytes() instruction as shown
in the sample code below.
for i = 1 to k
MoveBytes (InverseFloat(i),2,Float(i),0,2)
MoveBytes (InverseFloat(i),0,Float(i),2,2)
next
In the example above, InverseFloat(i) is the array holding the inverse-byte ordered
word (CDAB). Array Float(i) holds the obverse-byte ordered word (ABCD).
8.6.2.4 Troubleshooting
Test Modbus functions on the CR3000 with third party Modbus software. Further
information is available at the following links:
• www.simplyModbus.ca/FAQ.htm
• www.Modbus.org/tech.php
• www.lammertbies.nl/comm/info/modbus.html