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4. Repeat step 3 until 8 shifts have been performed. When this is done, a complete
8-bit byte will have been processed.
5. Repeat step 2 through 5 for the next 8-bit byte of the message. Continue doing this
until all bytes have been processed.
6. The final content of the CRC register is the CRC value. The CRC field is appended to
the message as the last field in the message. When this is done, the low-order byte
of the field is appended first, followed by the high-order byte.
The CRC high-order byte is the last byte to be sent in the message.
5.6 Transmission Control Procedure
1. Transmission procedure of master station
The master station must proceed to a communication upon conforming to the
following items.
1-1. Before sending a command message, provide 44 bits time or more vacant
status.
1-2. For sending, the interval between bytes of a command message is below 22
bits time.
1-3. Within 22 bits time after sending a command message, the receiving status is
posted.
1-4. Provide 44 bits time or more vacant status between the end of response
message reception and beginning for next command message sending (same
as in 1-1).
1-5. For ensuring the safety, make a confirmation of the response message and
make an arrangement so as to provide 3 or more retries in case of no response,
error occurrence, etc.
Note: The above definition is for most unfavorable value. For ensuring the safety,
it
＇
s recommended the program of the master to work with safety factors of
2 to 3. Concretely, it is advised to arrange the program for 9600 bps with
10ms or more for vacant status (1-1), and within 1ms for byte interval (1-2)
and changeover from sending to receiving (1-3).
2. Description
(1). Detection of the message frame Since the communication system uses the
2-write RS-485 interface, there may be 2 statuses on a line below.
(a) Vacant status (no data on line)
(b) Communication status (data is existing) Instruments connected on the line
are initially at a receiving status and monitoring the line. When 22 bits time
or more vacant status has appeared on the line, the end of preceding frame
is assumed and, within following 22 bits time, a receiving status is posted.
When data appears on the line, instruments receive it while 22 bits time or
