Code Name
Meaning
2
Illegal data
address
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, a request with offset
96 and length 4 would succeed, a request
with offset 96 and length 5 generates
exception 02.
3
Illegal data
value
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.
4
Slave device
failure
An unrecoverable error occurred while the
server (or slave) was attempting to
perform the requested action.
Table 8.21 Modbus Exception Codes
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
message. The parameter number is translated to Modbus
as (10 x parameter number) DECIMAL.
8.9.2 Storage of Data
The Coil 65 decimal determines whether data written to
the frequency converter are stored in EEPROM and RAM
(coil 65=1) or only in RAM (coil 65=0).
8.9.3 IND
The array index is set in Holding Register 9 and used when
accessing array parameters.
8.9.4 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 space
filled.
8.9.5 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. Refer to the
7.4 Quick Menu Parameters
.
8.9.6 Parameter Values
Standard data types
Standard data types are int16, int32, uint8, uint16 and
uint32. 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 2 registers
(32 bits). Readable sizes range from 1 register (16 bits) up
to 10 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 1 register (2 characters) up to 10 registers (20
characters).
8.10 Examples
The following examples illustrate various Modbus RTU
commands. If an error occurs, refer to
8.8.11 Modbus
Exception Codes
.
8.10.1 Read Coil Status (01 HEX)
Description
This function reads the ON/OFF status of discrete outputs
(coils) in the frequency converter. Broadcast is never
supported for reads.
Query
The query message specifies the starting coil and quantity
of coils to be read. Coil addresses start at zero, that is, coil
33 is addressed as 32.
Example of a request to read coils 33-48 (Status Word)
from slave device 01.
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