7.1 General serial communications 91
7.2 Modbus communications 92
7.2.1 About Modbus 93
7.2.2 Modbus protocols 94
7.2.3 Understanding Modbus Terminology 95
7.2.4 Connecting Modbus devices 95
7.2.5 Modbus master-slave protocol 95
7.2.6 About Modbus programming 96
7.2.6.1 Endianness 96
7.2.6.2 Function codes 97
7.2.7 Modbus information storage 98
7.2.7.1 Registers 98
7.2.7.2 Coils 98
7.2.7.3 Data Types 99
Unsigned 16-bit integer 99
Signed 16-bit integer 99
Signed 32-bit integer 100
Unsigned 32-bit integer 100
32-Bit floating point 100
7.2.8 Modbus tips and troubleshooting 100
7.2.8.1 Error codes 100
Result code -01: illegal function 100
Result code -02: illegal data address 101
Result code -11: COM port error 101
7.3 Internet communications 101
7.3.1 IPī£address 102
7.3.2 HTTPS 102
7.4 DNP3 communications 102
7.5 Serial peripheral interface (SPI) and I2C 103
7.6 PakBus communications 103
7.7 SDI-12 communications 104
7.7.1 SDI-12 transparent mode 104
7.7.1.1 SDI-12 transparent mode commands 106
7.7.2 SDI-12 programmed mode/recorder mode 106
7.7.3 Programming the data logger to act as an SDI-12 sensor 107
7.7.4 SDI-12 power considerations 107
Table of Contents - v
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