Rockwell-automation 900 Temperature Controller Communications Function Manual de usuario descargar pdf (Pagina 59)

4-1 Publication 900-UM004D-EN-E - July 2010

Chapter

Modbus Communications Procedure

Read this section if you are to communicate using the Modbus format.

Data Format

The data format complies with the Modbus (RTU) communications protocol,

so commands from the host computer and responses from the 900-TC8,

900-TC16, or 900-TC32 are contained in data blocks called frames.

The structure of the command and response frames is described below.

In the following explanations, hexadecimal values are expressed by adding the

prefix H’ before the number, e.g., H’02. Numbers and alphabetic characters

without the H’ prefix are ASCII characters.

Command Frame

When using RTU mode, start with a silent interval of at least 3.5 character

times and end with a silent interval of at least 3.5 character times.

Figure 4.1

CRC-16

Data

CRC-16 calculation range

2 bytes

Slave

address

Function

code

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 102 103

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Rockwell-automation 900 Temperature Controller Communications Function Manual de usuario Pagina 59