Omron V550-A20, Руководство по эксплуатации

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7
V550-A20 Operation Manual
Section 5-
7
Appendices
B Maximum: 4 character times (40/baud rate).
Minimum: 2 character times (due to guard
cha STX transmission time).
C Maximum: 1/2 character time (5/baud rate).
Minimum: 0.
Both the master and the slave must disable their transmitter as soon as
possible after transmitting the carriage return at the end of the message. The
transmitter must remain enabled while the carriage return is being sent out,
however. This means that the transmitting device must wait for a “transmit-
ter empty” (as opposed to a “transmitter ready”) indication from the serial
port before disabling the transmitter.
This protocol has been designed for a "slow" master to communicate with a
"fast" slave. The only time-critical item for the master is for the master to
release control of the line immediately after spending a message to a slave.
While the slave must respond within a very short time window, there are not
such constraints on the master. The master may have any amount of time
between messages or between characters within its message.
Error Recovery
Error: The slave does not understand a poll message.
Recovery: None. The master will time out, waiting for the slave’s
response, then will go on to the next unit.
Error: The slave does not understand a data message from the mas-
ter.
Recovery:
The master will retransmit the data message again after
timing out while waiting for the acknowledgment.
Error: The master does not understand the slave’s acknowledgment
of a data message.
Recovery:
The master will retransmit the data message after timing
out while waiting for the acknowledgment. The slave will acknowl-
edge the retransmitted message and discard it, since the message will
have the same sequence number as the last message received.
Error: The master does not understand the slave’s data message
(response to a poll).
Recovery:
The master will time out waiting for the slave’s response,
then continue on to the next poll. Since the slave did not receive an
acknowledgment for the data message, it will retransmit the same
message in response to the next poll.