User`s guide

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CHAPTER 8 - CFW-08 OPTIONS AND ACCESSORIES
Address:
The master initiates the communication by sending one byte
with the address of the slave to which the message is
addressed. The slave initiates the message with its own
address. The master can also send a message destined to
address 0 (zero), which means that the message is destined
to all network slaves (broadcast). In this case no slave will
answer to the master.
Function code:
This field contains an only byte, where the master specifies
the type of service or the function requestedto the slave (read,
write, etc.).According to the protocol, each function is used to
access a specific data type. In the CFW-08 all data are
available as holding type registers (referenced from the
address 40000 or ‘4x’). Besides these registers, the inverter
status (enabled/disabled, with error/no error, etc) and the
command for the inverter (run/stop, run FWD/REV, etc.) can
also be accessed through the coils read/write functions or the
internal bits (referenced from the address 00000 or ‘0x’ on).
Data field:
This field has variable length. The format and the content of
this field depend on the used function and transmitted values.
This field and the respective functions are described in item
8.25.3.
CRC:
The last part of the message is the field for checking the
transmission errors. The used method is the CRC-16 (Cycling
RedundancyCheck). This field is formed by two bytes, where
the least significant byte (CRC-) is transmitted first and only
then the most significant byte is transmitted (CRC+).
CRC calculation is started by loading a 16-bit variable
(mentioned from now on as CRC variable) with FFFFh value.
Then following steps are executed with the following routine:
1.
The first message byte (only the data bits - the start bit,
paritybitand stopbit are not used) is submitted to theXOR
logic (OR exclusive) with the 8 least significant bits of the
CRC variable, returning the result to the CRC variable,
2.
Then the CRCvariable is displaced one position to the right,
in the direction of the least significant bit and the position
of the most significant bit is filled out with zero 0 (zero).
3.
After this displacement, the flag bit (bit that has been
displaced out the CRC variable)is analyzed, byconsidering
the following:
If the bit value is 0 (zero), no change is made.
Ifthe bitvalue is 1, the CRC variable contentis submitted
to XOR logic with a constantA001h value and the value
is returned to the CRC variable.