User Manual

2 Protocol description
10
2.4.1 Timing of a data request
Timing
scheme
A data request runs according to the following timing scheme:
t
0
End marker = 3 characters
(the time depends on the baud rate)
t
1
This time depends on the internal processing.
The maximum processing time is 250 msec.
The minimum response time which can be set is required by the
RS485 interface in the master, in order to switch over the interface
driver from transmit to receive. This parameter is not required for
the RS422 interface.
t
2
This time is needed by the controller, to switch over from transmit
back to receive. This is the waiting time which the master has to
observe before presenting a new data request. This time must
always be observed, even when the new data request is directed to
another device.
RS422 interface: t
2
= 1msec
RS485 interface: t
2
= 10msec
H
A minimum response time can be set in the controller, under
the menu item “Interface”. This preset time is the minimum
time which will be waited before an answer is transmitted
(0 — 500 msec). If a smaller value is set, then the response
time may be longer than the preset value (because the
internal processing time is longer), the controller answers as
soon as the internal processing is completed. A preset time
of 0 msec means that the controller answers with the
maximum possible speed.
DatenanfrageMaster
Slave
t
Datenanfrage
Antwort
t
2
t
0
t
1
t
0
Master
Slave
Data request
Data request
Response