Savin P7026 Manual de usuario descargar pdf (Pagina 74)

PET-70216/ET-7026 User Manual, version 1.0.1 beta1, Page: 74

4.2.2. Function Codes

The second byte in the frame structure is the function code. The function code

describes what the slave is required to do. Valid function codes are between 1 and

255. The slave uses the same function code as the request to answer it. Only when

error occurs in the system, the highest bit of the function code will be made „1‟. Hence

the master will know if the message has been transmitted correctly or not.

Code

Function

Reference

01 (01H)

Read Coils (Output) Status

0xxxx

02 (02H)

Read Input Status

1xxxx

03 (03H)

Read Holding Registers

4xxxx

04 (04H)

Read Input Registers

3xxxx

05 (05H)

Force Single Coil (Output)

0xxxx

06 (06H)

Preset Single Register

4xxxx

15 (0FH)

Force Multiple Coils (Outputs)

0xxxx

16 (10H)

Preset multiple Registers

4xxxx

4.2.3. Data Field

The data field consists of messages sent between master and slave. The messages

contain additional information about the action to be taken by the slave or any

information requested by the slave. When the slave does not require this information

the data field can be nonexistent.

4.2.4. Error Check

The error check performed in Modbus/RTU is Cyclic Redundancy Check (CRC). Both

the transmitting device and the receiver compute CRC. Two bytes are used for this

purpose and generally one bit errors are detected by this method.

1 2 ... 69 70 71 72 73 74 75 76 77 78 79 ... 121 122

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