Dwyer UXF3 - Manual (Page 17)

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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 48 bits time or more vacant status.
(1-2) For sending, the interval between bytes of a command message is below 24 bits time.
(1-3) Within 24 bits time after sending a command message, the receiving status is posted.
(1-4) Provide 48 bits time or more vacant status between the end of response message reception and
beginning of 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 10 ms or more for vacant status (1-1), and within 1 ms for byte interval
(1-2) and changeover from sending to receiving (1-3).
(2) Description
1) Detection of the message frame
This communication system 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 24 bits
time or more vacant status has appeared on the line, the end of preceding frame is assumed and, within
following 24 bits time, a receiving status is posted. When data appears on the line, instruments receive it
while 24 bits time or more vacant status is detected again, and the end of that frame is assumed. I.e., data
which appeared on the line from the first 24 bits time or more vacant status to the next 24 bits time or more
vacant status is fetched as one frame.
Therefore, one frame (command message) must be sent upon confirming the following.
(1-1) 48 bits time or more vacant status precedes the command message sending.
(1-2) Interval between bytes of 1 command message is smaller than 24 bits time.
2) Response of this instrument (UXF3)
After a frame detection (24 bits time or more vacant status), this instrument carries out processing with that
frame as a command message. If the command message is destined to the own station, a response
message is returned. Its processing time is 5 to 60 ms (depends on contents of command message).
After sending a command message, therefore, the master station must observe the following
(1-3) Receiving status is posted within 24 bits time after sending a command message.
Bulletin F-107-UXF3-S