Siemens SIMOVERT MASTERDRIVES Manual page 250

Communication / USS
Start interval
STX LGE ADR 1.
Master transmits
Start
pause
BCC
Reply delay time
8.1-6
The STX start character (= 02 hexadecimal) by itself is not sufficient for
the slaves to clearly identify the start of a telegram because the bit
combination 02/hexadecimal can also occur in the net characters. For
this reason, a no-character start interval of at least 2 character run-
times before the STX is specified for the master. The start interval is
part of the task telegram.
Baud rate in bit/s
9600
19200
38400
76800
93750
187500
Table 8.1-1 Minimum start intervals for various baud rates
Only an STX with a preceding start interval identifies the valid start of a
telegram.
Data is always transferred in accordance with the diagram illustrated
below (half-duplex mode):
n BC C
Reply delay
Fig. 8.1-6 Transmit sequence
The time interval between the last character of the task telegram (BCC)
and the start of the reply telegram (STX) is known as the reply delay
time. The maximum permissible reply delay time is 20 ms, but it must
not be less than the start interval. If node x does not respond within
the maximum permissible reply delay time, an error message is
deposited in the master.
The master than sends the telegram for the next slave node.
Start interval in ms
2,30 ms
1,15 ms
0,58 ms
0,29 ms
0,23 ms
0,12 ms
Slave transmits
time
STX LGE ADR 1.
6SE7087-6QX70 (Version AD)
Compendium Motion Control
02.2004
STX
Start
pause
BCC
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SIMOVERT MASTERDRIVES