Danfoss VLT AutomationDrive FC 301 Series Design Manual page 203

RS-485 Installation and Set...
Code Name Meaning
2 Illegal data The data address received in the query is
address not an allowable address for the server
(or follower). 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 generates
exception 02.
3 Illegal data A value contained in the query data field
value 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 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.
4 Follower An unrecoverable error occurred while the
device failure server (or follower) was attempting to
perform the requested action.
Table 12.19 Modbus Exception Codes
12.12 How to Access Parameters
12.12.1 Parameter Handling
The PNU (Parameter Number) is translated from the
register address contained in the Modbus read or write
message. The parameter number is translated to Modbus
as (10 x parameter number) DECIMAL. Example: Reading
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 3-14 Preset Relative Reference (32 bit): The holding
registers 3410 and 3411 hold the parameters value. A
value of 11300 (Decimal) means that the parameter is set
to 1113.00.
For information on the parameters, size and converting
index, consult the product relevant programming guide.
12.12.2 Storage of Data
The Coil 65 decimal determines whether data written to
the adjustable frequency drive are stored in EEPROM and
RAM (coil 65=1) or only in RAM (coil 65=0).
MG33BF22
Design Guide
12.12.3 IND (Index)
Some parameters in the adjustable frequency drive are
array parameters, e.g., 3-10 Preset Reference. Since the
Modbus does not support arrays in the holding registers,
the adjustable frequency drive has reserved the holding
register 9 as pointer to the array. Before reading or writing
an array parameter, set the holding register 9. Setting
holding register to the value of 2 causes all following read/
write to array parameters to be to the index 2.
12.12.4 Text Blocks
Parameters stored as text strings are accessed in the same
way as the other parameters. The maximum text block size
is 20 characters. If a read request for a parameter is for
more characters than the parameter stores, the response is
truncated. If the read request for a parameter is for fewer
characters than the parameter stores, the response is
padded with spaces.
12.12.5 Conversion Factor
The different attributes for each parameter can be seen in
the section on factory settings. Since a parameter value
can only be transferred as a whole number, a conversion
factor must be used to transfer decimals.
12.12.6 Parameter Values
Standard data types
Standard data types are int 16, int 32, uint 8, uint 16 and
uint 32. They are stored as 4x registers (40001–4FFFF). The
parameters are read using function 03hex "Read Holding
Registers." Parameters are written using the function 6hex
"Preset Single Register" for 1 register (16 bits), and the
function 10 hex "Preset Multiple Registers" for two registers
(32 bits). Readable sizes range from one register (16 bits)
up to ten registers (20 characters).
Non-standard data types
Non-standard data types are text strings and are stored as
4x registers (40001–4FFFF). The parameters are read using
function 03hex "Read Holding Registers" and written using
function 10hex "Preset Multiple Registers." Readable sizes
range from one register (two characters) up to ten
registers (20 characters).
Rev. 2014-04-04 All rights reserved.
12 12
201