6.6.3 Switch-closure and open-collector measurements 74
6.6.3.1 P Terminals 74
6.6.3.2 C terminals 75
6.6.4 Edge timing and edge counting 75
6.6.4.1 Single edge timing 75
6.6.4.2 Multiple edge counting 75
6.6.4.3 Timer input NAN conditions 75
6.6.5 Quadrature measurements 76
6.6.6 Pulse measurement tips 77
6.6.6.1 Input filters and signal attenuation 77
6.6.6.2 Pulse count resolution 77
6.7 Vibrating wire measurements 78
6.7.1 VSPECT® 78
6.8 Sequential and pipeline processing modes 78
6.8.1 Sequential mode 79
6.8.2 Pipeline mode 79
6.8.3 Slow Sequences 80
7. Communications Protocols 81
7.1 General serial communications 82
7.2 Modbus communications 82
7.2.1 About Modbus 83
7.2.2 Modbus protocols 84
7.2.3 Understanding Modbus Terminology 85
7.2.4 Connecting Modbus devices 85
7.2.5 Modbus master-slave protocol 86
7.2.6 About Modbus programming 86
7.2.6.1 Endianness 87
7.2.6.2 Function codes 87
7.2.7 Modbus information storage 88
7.2.7.1 Registers 88
7.2.7.2 Coils 88
7.2.7.3 Data Types 89
Unsigned 16-bit integer 89
Signed 16-bit integer 89
Signed 32-bit integer 89
Unsigned 32-bit integer 90
Table of Contents - iv
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