13
Chapter 4. Communication
Timing specifications for command and response messages
When the master and slave stations are connected directly with RS-485, the
following points regarding the timing of command/response messages from the
master/slave stations must be observed.
z
Response monitoring time
The maximum response time from the end of command message transmission by
the master station to the start of response message reception from the slave station
is 2 seconds (#1 in the figure below).
Therefore, the response monitor time should be set to 2 seconds.
If a response time-out occurs, the command message should be resent.
z
Transmission start time
After the master station finishes receiving a response message (#2 in the figure
below), a wait time of 10 ms is required before it begins to transmit a command
message (to the same or a different slave station).
RS-485 driver control timing specifications
When the transmission/reception on a 3-wire RS-485 system is directly controlled
by the master station, care should be paid to the timing shown below.
Command
message
Transmission
line
RS-485 3-wire system
Command
message
Response
message
(1) End of master station transmission − Start of slave station transmission = 2000 ms max.
(2) End of slave station transmission − Start of master station transmission = 10 ms min.
Response
message
(1) (2)
(enable)
(enable)
(disable)
(disable)
Master station
driver control
Slave station
driver control
Transmission
line
(command message)
Valid
data
Valid
data
(1) End of master station transmission − Master station driver disabled time = 500 μs max.
(2) End of slave station reception − Slave station driver enabled time = 1 ms or more
(3) End of slave station transmission − Slave station driver disabled time = 10 ms or less
(4) End of master station reception − Master station driver enabled time = 10 ms or more
End of master station transmission
End of slave station transmission
(response message)
(1)
(4)
(2)
(3)
4 - 4 Timing Specifications
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