ProSoft Technology 5202-DFNT-MCM4 - Manual (Page 69)

Reference MCM ♦ ProLinx Gateway
Driver Manual Modbus Master/Slave
ProSoft Technology, Inc.
Page 69 of 80
October 16, 2009
If the output address is non-existent in the server device, the server will return
the exception response with the exception code shown (02). This specifies an
illegal data address for the Slave.
Modbus Exception Codes
Code Name Meaning
01 Illegal Function The function code received in the query is not an allowable
action for the Slave. This may be because the function code is
only applicable to newer devices, and was not implemented in
the unit selected. It could also indicate that the Slave is in the
wrong state to process a request of this type, for example
because it is unconfigured and is being asked to return register
values.
02 Illegal Data Address The data address received in the query is not an allowable
address for the Slave. More specifically, the combination of
reference number and transfer length is invalid. For a controller
with 100 registers, a request with offset 96 and length 4 would
succeed; a request with offset 96 and length 5 will generate
exception 02.
03 Illegal Data Value A value contained in the query data field is not an allowable
value for Slave. This indicates a fault in the structure of the
remainder of a complex request, such as that the implied length
is incorrect. It specifically does not mean that a data item
submitted for storage in a register has a value outside the
expectation of the application program, because the Modbus
protocol is unaware of the significance of any particular value of
any particular register.
04 Slave Device Failure An unrecoverable error occurred while the Slave was attempting
to perform the requested action.
05 Acknowledge Specialized use in conjunction with programming commands.
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 timeout error from occurring in the Master.
The Master can next issue a poll program complete message to
determine if processing is completed.
06 Slave Device Busy Specialized use in conjunction with programming commands.
The Slave is engaged in processing a long-duration program
command. The Master should retransmit the message later
when the Slave is free.
08 Memory Parity Error Specialized use in conjunction with function codes 20 and 21
and reference type 6, to indicate that the extended file area
failed to pass a consistency check. The Slave attempted to read
record file, but detected a parity error in the memory. The
Master can retry the request, but service may be required on the
server Slave device.
0a Gateway Path
Unavailable
Specialized use in conjunction with gateways, indicates that the
gateway was unable to allocate an internal communication path
from the input port to the output port for processing the request.
Usually means that the gateway is misconfigured or overloaded.
0b Gateway Target
Device Failed To
Respond
Specialized use in conjunction with gateways, indicates that no
response was obtained from the target device. Usually means
that the device is not present on the network.