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Page 8 - 6739389EN/FB
Checking received
messages on the slave
side
After the master sends a request
containing the slave address, the
function code and data, it computes
the CRC and sends it as the check
word (CRC 16).
When the slave receives the
request, it stores the message in
memory and calculates the CRC 16
to compare it to the received CRC
16.
master
slave
CRC 16 comparison
CRC 16
function
slave address
data
CRC 16
computation
If the message is incorrect (unequal
CRC 16 values), the slave does
not respond.
If the message received is correct
but the slave is unable to process it
(incorrect address, incorrect data,
etc.), the slave returns an error
message with the following
contents (see opposite):
1
function code
received and
MS bit = 1
Error codes:
1. Unknown function code
2. Incorrect address
3. Incorrect data
4. Station not ready
8. Write error
9. Field overlap
1 byte 1 byte 1 byte
CRC 16
response
request
01
09
H
00 0000 00 DD CB
01
89
H
01 86 50
response
example
2 bytes
errors handled
by the
communication
port
slave
address
(1 à FF)
JBUS protocol (continued)