Crc Generation; Input Parameters - Hitachi Abb Rvt Installation Und Betriebsanleitung

01 ILLEGAL FUNCTION
02 ILLEGAL DATA ADDRESS
03 ILLEGAL DATA VALUE
04 SLAVE DEVICE ABORT
05 ACKNOWLEDGE
06 SLAVE DEVICE BUSY
07 NEGATIVE ACKNOWLEDGE
08 MEMORY PARITY ERROR
An application program in the master is responsible for handling exception responses. Typical processes include suc-
cessive attempts to send a query, sending diagnostic messages to the slave, and notifying the operators.
3.9.

CRC generation

The Cyclical Redundancy Check (CRC) field is two bytes, containing a 16–bit binary value. The CRC value is calcu-
lated by the transmitting device, which appends the CRC to the message. The receiving device recalculates a CRC
during receipt of the message, and compares the calculated value to the actual value it received in the CRC field. If
the two values are not equal, an error results.
Placing the CRC into the Message:
When the 16–bit CRC (two 8–bit bytes) is transmitted in the message, the low-order byte will be transmitted first, fol-
lowed by the high-order byte.
Example: here is an example of calculating directly the CRC.
/*-----------------------------------------------------------------
FUNCTION
-----------------------------------------------------------------

INPUT PARAMETERS :

-----------------------------------------------------------------
OUTPUT
-----------------------------------------------------------------
STATUS
Approved
The function code received in the query is not an allowable action
for the slave device (see paragraph 2.2).
The data address or number of items received in the query is not
allowable or correct for the slave device. The slave device will
send this exception response if an attempt to read or write part of
a multiple register database object is detected. Possible objects
are time, strings and counters
A value contained in the query data field is out of range. The con-
tents of the register or the status of the coil has not changed (see
paragraph 4.3).
An unrecoverable error occurred while the slave was attempting
to perform the requested action. This may happen when the ac-
cess level for changing a parameter is not reached (see para-
graph 4.2.)
Not supported
Not supported
Not supported
Not supported
: This routine calculates the crc high and low byte of a message.
buf -> Array containing message to be sent to controller
start -> Start of loop in crc counter, usually 0.
cnt -> Amount of bytes in message being sent to controller
: temp -> Returns crc byte for message.
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DOCUMENT ID
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RVT CO MM UNI CATI O N
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