Lika SMAX-AI1-PRG-L2, User Manual

Page: 52 / 84

SMAX MODBUS®
Request PDU
Function code 1 byte 04 hex
Starting address 2 bytes 0000 hex to FFFF hex
Quantity of Input Registers 2 bytes 0000 hex to 007D hex
Response PDU
Function code 1 byte 04 hex
Byte count 1 byte
2 x
N*
Input register value N*
x 2 bytes
*N = Quantity of registers
Exception Response PDU
Error code 1 byte 84 hex (=04 hex + 80 hex)
Exception code 1 byte 01 or 02 or 03 or 04
Here is an example of a request to read the Current position [0001 hex]
parameter (input register 2).
Request Response
Field name (Hex) Field name (Hex)
Function 04 Function 04
Starting address Hi 00 Byte count 02
Starting address Lo 01 Register 2 value Hi 13
Quantity of Input Reg. Hi 00 Register 2 value Lo C5
Quantity of Input Reg. Lo 01
As you can see in the table,
Current position [0001 hex]
parameter (input
register 2) contains the value 13 C5 hex, i.e. 5061 in decimal notation.
The full frame needed for the request to read the
Current position [0001 hex]
parameter (input register 2) to the Slave having the node address 1 is as follows:
MAN SMAX MB E 1.2 Modbus® interface 52 of 84