Ados A100E - Bi-Directional Modality with MODBUS Protocol

ADOS S.R.L. Buccinasco (MI)
492-MTU10006 Rev. 4 Page 19 of 49
3.11.6 Bi-directional modality with MODBUS protocol
The RTU version of MODBUS is used.
Received and transmitted frame structure
General frame structure is as follows:
ADDRESS FUNCTION DATA CHECK
8 bits 8 bits N x 8 bits 2 x 8 bits
ADDRESS 8 bit defining the slave address and ranging from 1 to 32
FUNCTION 8 bit defining the required function.
The functions supported by A100E are the following
Code 03 Read Holding Registers
Code 05 Force Single Coil
Code 06 Preset Single Register
Code 16 Preset Multiple Registers
DATA All data relevant to the specific function
CHECK CRC-16 (Cyclic Redundancy Check) frame validation
Exception responses
When A100E receives a request involving illegal functions or illegal data an exception response is generated
containing address, function code, error code and checksum.
To indicate that the response is a notification of an error, the high order bit of the function code is set to “1”.
Supported error code are:
01 Illegal function. The message function received is not an allowable action for the
addressed slave.
02 Illegal data address. The address referenced in the data field is not an allowable
address in the address slave location
03 Illegal data value. The value referenced in the data field is not allowable in the
addressed slave location
A100E supported functions
For a complete description of MODBUS available functions, please refer to detailed MODBUS
documentation.
Function 03 - Read Holding Registers