User`s manual

161
04
Read Input Registers
Read data in 16-bits register format
05
Write Coil
Write data to force a digital output ON/OFF
06
Write Single Register
Write data in 16-bits register format
15
Force Multiple Coils
Write data to force multiple consecutive
coils
The MDI-110 device supports the function code 04, which name is Read Input
Registers. With this support, the remove SCADA or other Modbus TCP application
can poll the information of the device and monitor the major status of the switch.
5.3.2 Error Checking
The utilization of the error checking will help eliminate errors caused by noise in the
communication link. In Modbus TCP mode, messages include an error-checking field
that is based on a Cyclical Redundancy Check (CRC) method. The CRC filed checks the
contents of the entire message. It applied regardless of any parity check method
used for the individual BYTE actors of the message. The CRC value is calculated by
the transmitting device, which appends the CRC to the message. The receiving
device recalculates a CRC during receipt of the message, and compares the
calculated value to the actual value it received in the CRC filed.
5.3.3 Exception Response
If an error occurs, the slave sends an exception response message to master
consisting of the slave address, function code, exception response code and error
check field. In an exception response, the slave sets the high-order bit (MSB) of the
response function code to one. The exception response codes are listed below.
Code
Name
Descriptions
01
Illegal Function
The message function received is not allowable
action.
02
Illegal Data Address
The address referenced in the data field is not
valid.
03
Illegal Data Value
The value referenced at the addressed device
location is no within range.
04
Slave Device Failure
An unrecoverable error occurred while the
slave was attempting to perform the
requested action.
05
Acknowledge
The slave has accepted the request and
processing it, but a long duration of time will
be required to do so.
06
Slave Device Busy
The slave is engaged in processing a
long-duration program command.