Network Card User Manual

Connection Example

890USE17700 April 2004 147

Request and

Response

Example

The following example uses the data from channel 1 and channel 2 in the

STB AVO 1250 module (node 8 in the sample Advantys STB island bus) (See

Example, p. 142). In the example, Modbus register 40004 corresponds to channel 1

and Modbus register 40005 corresponds to channel 2.

Request: The request determines the starting address and the number of registers

to be read. In this case, two registers—40004 and 40005—should be read:

Response: The response is the reply from the device. It contains the contents of the

registers in which the requested data is located. In this case, register 40004 contains

data 1234, and register 40005 contains data 6789:

Reference

Descriptions

The x’s following the leading character (3/4) represent a four-digit Modbus register

address:

3xxxx

Read input registers. A 3x reference register contains a 16-bit number received

from an external source, e.g., an analog signal.

4xxxx

Read/write output or holding registers. A 4x reference register is used to store 16-

bits of numerical data (binary or decimal), or to send the data from the CPU to an

output channel.

Note: The examples use hexadecimal notation (0x000) for their numerical format.

Addressing begins in the output process image at register 40001. The format and

addressing may vary according to your particular software and controls.

Description Field Example

command Modbus function code 0x003

starting point starting register 0x40004

Description Field Example

command Modbus function code 0x003

returned value value of register 40004 0x1234

returned value value of register 40005 0x6789