Table 68: Function Codes
Function
Function code
Subfunction code
Subfunction
Diagnostics
8
1
Restart communication.
2
Return diagnostic register.
10
Clear counters and diagnostic register.
11
Return bus message count.
12
Return bus communication error count.
13
Return follower error count.
14
Return follower message count.
8.8.10.3 Modbus Exception Codes
For a full explanation of the structure of an exception code response, refer to
.
Table 69: Modbus Exception Codes
Code Name
Meaning
1
Illegal func-
tion
The function code received in the query is not an allowable action for the server (or follower). 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 follower) is in the wrong state to process a request of
this type, for example because it is not configured and is being asked to return register values.
2
Illegal data
address
The data address received in the query is not an allowable address for the server (or follower). More spe-
cifically, the combination of reference number and transfer length is invalid. For a controller with 100
registers, a request with offset 96 and length 4 succeeds, while a request with offset 96 and length 5 gen-
erates exception 02.
3
Illegal data
value
A value contained in the query data field is not an allowable value for server (or follower). This indicates a
fault in the structure of the remainder of a complex request, such as that the implied length is incorrect.
It 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 value of any
register.
4
Follower de-
vice failure
An unrecoverable error occurred while the server (or follower) was attempting to perform the requested
action.
8.9 How to Access Parameters
8.9.1 Parameter Handling
The PNU (parameter number) is translated from the register address contained in the Modbus read or write telegram. The parame-
ter number is translated to Modbus as (10 x parameter number) decimal.
Examples
Reading
parameter 3-12 Catch up/slow Down Value
(16 bit): The holding register 3120 holds the parameters value. A value of 1352
(decimal), means that the parameter is set to 12.52%.
Reading
parameter 3-14 Preset Relative Reference
(32 bit): The holding registers 3410 and 3411 hold the parameters values. A value of
11300 (decimal), means that the parameter is set to 1113.00.
For information on the parameters, size, and conversion index, see the drive's Programming Guide.
8.9.2 Storage of Data
The coil 65 decimal determines whether data written to the drive is stored in EEPROM and RAM (coil 65 = 1), or only in RAM (coil 65
= 0).
AJ363928382091en-000101 / 130R0983
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RS485 Installation and Set-up
VLT® Flow Drive FC 111
Design Guide