Campbell CR6 Series, Руководство оператора

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Section 8. Operation
529
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
8.10.3.2.5 Reading Inverse Format Modbus 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 CR6
uses the ABCD format, either the master has to make an adjustment, which is
sometimes possible, or the CR6 needs to output reverse-byte order words. To
reverse the byte order in the CR6, 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).
See Endianness
(p. 649).
8.10.3.2.6 Timing
The timeout is a critical parameter of Modbus communication. The response time
of devices is usually not specified by the manufacturer and can range from 100 ms
to more than 5 seconds. When the CR6 is acting as a slave device, it typically
responds very quickly. The default timeout in a master device polling the CR6
will typically not need adjustment from the default. When the CR6 is acting as a
master, the response time of a slave needs particular attention. The best practice is