Watlow CLS200, MLS300 and CAS200 User Manual Page 27
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Chapter 2: Modbus-RTU Protocol
Communications Specification 21
Chapter 2: Modbus-RTU Protocol
Overview
Transactions on Modbus-RTU Networks
Standard Modbus-RTU ports use an EIA/TIA-232C- or EIA/TIA-485/
422-compatible serial interface that defines connector pinouts, cabling,
signal levels, transmission baud rates, and parity checking.
Controllers communicate using a master-slave technique, in which only
one device (the master) can initiate transactions (called “queries”). The
other devices (slaves) respond by supplying the requested data to the
master, or by taking the action requested in the query. Typical master
devices include host processors and programming panels.
The master can address individual slaves, or initiate a broadcast
message to all slaves. Slaves return a message (called a “response”) to
queries that are addressed to them individually. Responses are not
returned to broadcast queries from the master.
The Modbus-RTU protocol establishes the format for the master’s query
by placing into it the device (or broadcast) address, a function code
defining the requested action, any data to be sent, and an error-checking
field. The slave’s response message is also constructed using Modbus-
RTU protocol. It contains fields confirming the action taken, any data to
be returned, and an error-checking field. If an error occurred in receipt
of the message, or if the slave is unable to perform the requested action,
the slave will construct an error message and send it as its response.
- CLS200, MLS300 1
- Communications 1
- Specification 1
- Warranty 2
- Contents 3
- Protocol Syntax 9
- Transaction Sequence 10
- Packet Format 12
- Codes in a Packet 12
- Error Checking 14
- Cyclic Redundancy Check (CRC) 15
- Examples 16
- Block Write 19
- Message Data 20
- Data for a Write Command 21
- Two-Byte Data Types 21
- Figuring Block Size 21
- Anafaze/AB Data Table Summary 22
- Number Description 24
- Address 24
- Type Number of Bytes 24
- Overview 27
- The Query-Response Cycle 28
- Serial Transmission 28
- Message Framing 29
- Contents of the Data Field 30
- CRC Error Checking 31
- Function Codes 32
- Diagnostic Subfunctions 33
- Writing Data 36
- Reading Data 36
- Write Examples 38
- Modbus-RTU Data Table Summary 39
- Chapter 3: 45
- All Units 17, 18 47
- Enhanced Features options 49
- Parameters (by number) 51
- Input Type (3) 52
- Output Type (4) 53
- Setpoint (5) 54
- Process Variable (6) 54
- Output Filter (7) 54
- Output Value (8) 55
- Alarm Deadband (12) 55
- Alarm_Status (13) 56
- Ambient Sensor Readings (15) 58
- Pulse Sample Time (16) 58
- High Process Variable (17) 58
- Low Process Variable (18) 58
- Precision (19) 59
- Cycle Time (20) 60
- Zero Calibration (21) 60
- Full Scale Calibration (22) 60
- Digital Inputs (25) 60
- Digital Outputs (26) 61
- Override Digital Input (28) 61
- Override Polarity (29) 61
- System Status (30) 62
- System Command Register (31) 62
- Data Changed Register (32) 63
- Input Units (33) 63
- EPROM Version Code (34) 64
- Options Register (35) 64
- High Reading (37) 65
- Low Reading (38) 65
- Heat/Cool Spread (39) 65
- Startup Alarm Delay (40) 66
- • Range: See tables below 67
- • Default: 0 67
- Current Segment (47) 68
- Segment Time Remaining (48) 68
- Current Cycle Number (49) 68
- Tolerance Alarm Time (50) 68
- Last Segment (51) 68
- Number of Cycles (52) 69
- Ready Setpoint (53) 69
- Ready Event States (54) 69
- Segment Setpoint (55) 70
- Segment Time (58) 72
- Tolerance (59) 72
- Ramp/Soak Flags (60) 72
- Output Limit (61) 73
- Output Limit Time (62) 73
- Alarm_Control (63) 74
- Alarm_Acknowledge (64) 74
- Alarm_Mask (65) 74
- Alarm_Enable (66) 74
- AIM Fail Output (68) 75
- Output Linearity Curve (69) 76
- SDAC Mode (70) 76
- SDAC Low Value (71) 76
- SDAC High Value (72) 76
- Save Setup to Job (73) 77
- Input Filter (74) 77
- Loop Alarm Delay (75) 77
- Loop Names (77) 77
- Channel Name (78) 78
- Manufacturing Test (80) 78
- Cascade Maximum Setpoint (89) 80
- Cascade Base Setpoint (87) 80
- Cascade Minimum Setpoint (88) 80
- Loop Status (96) 82
- Output Type/Disable (97) 82
- Output Reverse/Direct (98) 82
- Controller Type (99) 83
- Ramp/Soak Profile Number (100) 83
- Controller Address (101) 83
- Baud Rate (102) 83
- Ready Events (103) 84
- Appendix A: 85
- Communications Driver 85
- Close_Comm_Port() 86
- DownLoad() 86
- UpLoad() 87
- Glossary 89
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