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
Summary of Contents for CR6 Series
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Page 76: ...Section 5 Overview 76 FIGURE 20 Half Bridge Wiring Example Wind Vane Potentiometer ...
Page 80: ...Section 5 Overview 80 FIGURE 23 Pulse Input Wiring Example Anemometer ...
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Page 454: ...Section 8 Operation 454 FIGURE 104 Narrow Sweep High Noise ...
Page 459: ...Section 8 Operation 459 FIGURE 106 Vibrating Wire Sensor Calibration Report ...
Page 535: ...Section 8 Operation 535 8 11 2 Data Display FIGURE 121 CR1000KD Displaying Data ...
Page 537: ...Section 8 Operation 537 FIGURE 123 CR1000KD Real Time Custom ...
Page 538: ...Section 8 Operation 538 8 11 2 3 Final Storage Data FIGURE 124 CR1000KD Final Storage Data ...
Page 539: ...Section 8 Operation 539 8 11 3 Run Stop Program FIGURE 125 CR1000KD Run Stop Program ...
Page 541: ...Section 8 Operation 541 FIGURE 127 CR1000KD File Edit ...
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Page 610: ...Section 11 Glossary 610 FIGURE 137 Relationships of Accuracy Precision and Resolution ...
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