5
3. If the LSB is 0: Shift the CRC register one bit to the right (toward the LSB),
Zero-filling the MSB.
If the LSB is 1: Shift the CRC register one bit to the right (toward the LSB),
Zero-filling the MSB. Exclusive OR the CRC registers with the polynomial value
A001 hex.
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 more vacant status is detected again, and the end of that
frame is assumed. Data, which appeared on the line from the first 44ms time or
more vacant status to the next 44 bits time or more vacant status is fetched as
one frame.
1-1. 44 bits time or more vacant status precedes the command message
sending.
1-2. Interval between bytes of 1 command message is smaller than 22 bits
time.
(2). Response of this instrument (SE series)
After a frame detection (22 bits time or more vacant status), this instrument
