ABB NMBA-01 Installation And Startup Manual page 56

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Appendix B – Modbus Protocol
B-18
In this example, the master addresses a query to slave device 10 (0A
hex). The function code (01) is for a Read Coil Status operation. It
requests the status of the coil at address 1245 (04A1 hex). Note that
only that one coil is to be read, as specified by the number of coils field
(0001).
If the coil address is non-existent in the slave device, the slave will
return the exception response with the exception code shown (02).
This specifies an illegal data address for the slave. For example, if the
slave is a 984-385 with 512 coils, this code would be returned.
A listing of Modicon exception codes is in Table C-1 Standard Excep-
tion Codes.
Table C-1 Standard Exception Codes
Code Name
01 ILLEGAL FUNCTION
02 ILLEGAL DATA
ADDRESS
03 ILLEGAL DATA VALUE
04 SLAVE DEVICE
FAILURE
05 ACKNOWLEDGE
06 SLAVE DEVICE BUSY
07 NEGATIVE
ACKNOWLEDGE
08 MEMORY PARITY
ERROR
Meaning
The function code received in the query is not
an allowable action for the slave. If a Poll
Program Complete command was issued, this
code indicates that no program function
preceded it.
The data address received in the query is not
an allowable address for the slave.
A value contained in the query data field is not
an allowable value for the slave.
An unrecoverable error occurred while the
slave was attempting to perform the requested
action.
The slave has accepted the request and is
processing it, but a long duration of time will be
required to do so. This response is returned to
prevent a time-out error from occurring in the
master. The master can next issue a Poll
Program Complete message to determine if
processing is completed.
The slave is engaged in processing a long
duration program command. The master
should retransmit the message later when the
slave is free.
The slave cannot perform the program function
received in the query. This code is returned for
an unsuccessful programming request using
function code 13 or 14 decimal. The master
should request diagnostic or error information
from the slave.
The slave attempted to read extended
memory, but detected a parity error in the
memory. The master can retry the request, but
service may be required on the slave device.
NMBA-01 Installation and Start-up Guide