Appendix D: Modbus Error Codes - Elpro Technologies 915U-2 User Manual

915U-2 Wireless I/O

Appendix D: Modbus Error Codes

Code Name
Illegal
0
Function
Illegal Data
02
Address
Illegal Data
03
Value
Slave Device
04
Failure
Acknowledge
05
Slave Device
06
Busy
Memory
08
Parity Error
Page 97
Meaning
The function code received in the query is not an allowable
action for the server (or 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
server (or slave) is in the wrong state to process a request of
this type.
The data address received in the query is not an allowable
address for the server (or slave). More specifically, the
combination of reference number and transfer length is invalid.
For a controller with 100 registers, the PDU addresses the first
register as 0, and the last one as 99. If a request is submitted
with a starting register address of 96 with a quantity of 4
registers, then this request will successfully operate on
registers 96, 97, 98, 99. If a request is submitted with a starting
register address of 96 and a quantity of registers of 5, then this
request will fail with Exception Code 0x02 "Illegal Data
Address".
A value contained in the query data field is not an allowable
value for server (or 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, since the MODBUS
protocol is unaware of the significance of any particular value
of any particular register.
An unrecoverable error occurred while the server (or slave)
was attempting to perform the requested action.
Specialized use in conjunction with programming commands.
The server (or 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 client (or master).
Specialized use in conjunction with programming commands.
The server (or slave) is engaged in processing a long–duration
program command. The client (or master) should retransmit
the message later when the server (or slave) is free.
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.
Page 97
User Manual