Siemens SIMATIC S7-1200 - Page 1152

Communication processor and Modbus TCP
13.4 Universal serial interface (USS) communication
S7-1200 Programmable controller
1152 System Manual, V4.2, 09/2016, A5E02486680-AK
Calculating the time required for communicating with the drive
Communications with the drive are asynchronous to the S7-1200 scan cycle. The S7-1200
typically completes several scans before one drive communications transaction is
completed.
The USS_Port_Scan interval is the time required for one drive transaction. The table below
shows the minimum USS_Port_Scan interval for each communication baud rate. Calling the
USS_Port_Scan FB more frequently than the USS_Port_Scan interval will not increase the
number of transactions. The drive timeout interval is the amount of time that might be taken
for a transaction, if communications errors caused 3 tries to complete the transaction. By
default, the USS protocol library automatically does up to 2 retries on each transaction.
Table 13- 41 Calculating the time requirements
Baud rate
Calculated minimum USS_Port_Scan call
Interval ( milliseconds )
Drive message interval timeout per
drive ( milliseconds )
1200
790
2370
2400 405 1215
4800
212.5
638
9600 116.3 349
19200
68.2
205
38400
44.1
133
57600
36.1
109
115200
28.1
85