Schneider Electric 890USE17700 manual Request, Response, Reference, Descriptions

			Connection Example
Request and	The following example uses the data from channel 1 and channel 2 in the
Response	STB AVO 1250 module (node 8 in the sample Advantys STB island bus) (See
Example	Example, p. 142). In the example, Modbus register 40004 corresponds to channel 1
	and Modbus register 40005 corresponds to channel 2.
	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.
	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:
	Description	Field		Example
	command	Modbus function code		0x003
	register count	word count		0x002
	starting point	starting register		0x40004
	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:
	Description	Field		Example
	command	Modbus function code		0x003
	register count	word count		0x002
	returned value	value of register 40004		0x1234
	returned value	value of register 40005		0x6789
Reference	The x’s following the leading character (3/4) represent a four-digit Modbus register
Descriptions	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.

890USE17700 April 2004 147