Modbus Protocol Specification
Chapter 2 Data and Control Functions
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- Điều hướng trang này:
- 2.1 Modbus Function Formats Note
- 2.1.2 Field Contents in Modbus Messages
| Chapter 2
Data and Control Functions V Modbus Function Formats V Function Codes V Read Coil Status V Read Input Status V Read Holding Registers V Read Input Registers V Force Single Coil V Preset Single Register V Read Exception Status V Fetch Comm Event Counter V Fetch Comm Event Log V Force Multiple Coils V Preset Multiple Registers V Report Slave ID V Read General Reference V Write General Reference V Mask Write 4x Register V Read / Write 4x Registers http://www.modicon.com/techpubs/dcon7.html (1 of 36) [1/11/2000 10:41:03 PM] V Read FIFO Queue 2.1 Modbus Function Formats Note: Unless specified otherwise, numerical values (such as addresses, codes, or data) are expressed as decimal values in the text of this section. They are expressed as hexadecimal values in the message fields of the figures. 2.1.1 Data Addresses in Modbus Messages All data addresses in Modbus messages are referenced to zero. The first occurrence of a data item is addressed as item number zero. For example: V Coil 1 in a programmable controller is addressed as coil 0000 in the data address field of a Modbus message V Coil 127 decimal is addressed as coil 007E hex (126 decimal) V Holding register 40001 is addressed as register 0000 in the data address field of the message. The function code field already specifies a holding register operation. Therefore the 4x reference is implicit. V Holding register 40108 is addressed as register 006B hex (107 decimal) 2.1.2 Field Contents in Modbus Messages The following tables show examples of a Modbus query and normal response. Both examples show the field contents in hexadecimal, and also show how a message could be framed in ASCII or in RTU mode. tải về 0.61 Mb. Chia sẻ với bạn bè của bạn:
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