Siemens RS-485 - Manual (Page 4)

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Siemens Building Technologies CC1A7865.1en
HVAC Products 31.10.2002
Data query sequence
The time sequence of a data query looks as follows:
Master
Slave
Data query
Reply
Data query
t 0 t 1 t 0 t 2 7865z12e/1102
t0 Identification of end = 3 characters
(time is dependent on the Baud rate)
t1 This time is dependent on internal handling.
The maximum handling time is 250 ms
t2 This is the time required by the device to switch from the transmitting mode back
to the receiving mode.
This time must be observed by the master before it makes a new data query. It
must always be maintained, even if the new data query is sent to some other
device.
t2 ³ 20 ms
Communication during the slave’s internal handling time
The master is not allowed to make any data queries during the slave’s internal handling
time.
Data queries made during that period of time will be ignored by the slave.
Communication during the slave’s response time
The master is not allowed to make any data queries during the slave’s response time.
Data queries made during that period of time cause all data currently on the bus to
become obsolete.
Time sequence