Siemens Simatic S7 Series System Manual

Libraries
9.2 USS library instructions
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
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9.2.1.3
Calculating the time required for communicating with the drive
Communications with the drive are asynchronous to the S7-200 SMART CPU scan. The
CPU typically completes several scans before one drive communications transaction is
completed. The following factors help determine the amount of time required:
● Number of drives present
● Baud rate
● Scan time of the CPU
Some drives require longer delays when using the parameter access instructions. The
amount of time required for a parameter access is dependent on the drive type and the
parameter being accessed.
After a USS_INIT instruction assigns Port 0 to use the USS Protocol (or USS_INIT_P1 for
port 1), the CPU regularly polls all active drives at the intervals shown in the following table.
You must set the time-out parameter of each drive to allow for this task:
Table 9- 1 Communications times
Baud rate
Time between polls of active drives
(with no parameter access instructions active)
1200
240 ms (maximum) times the number of drives
2400
130 ms (maximum) times the number of drives
4800
75 ms (maximum) times the number of drives
9600 50 ms (maximum) times the number of drives
19200
35 ms (maximum) times the number of drives
38400
30 ms (maximum) times the number of drives
57600
25 ms (maximum) times the number of drives
115200
25 ms (maximum) times the number of drives

Siemens Simatic S7 Series Specifications

General

CPU	Varies by model (e.g., S7-300, S7-400, S7-1200, S7-1500)
Communication Interfaces	PROFIBUS, PROFINET, Ethernet, MPI
Programming	TIA Portal, STEP 7
Programming Languages	LAD, FBD, STL, SCL, GRAPH
I/O Modules	Digital, Analog, Specialty modules available
Operating Temperature	0°C to 60°C (standard models)
Mounting	DIN rail mounting
Operating Voltage	24V DC or 120/230V AC (varies by model)
Protection Class	IP20 (standard models)
Memory	Varies depending on the S7 model. Includes work memory (RAM) for program execution, load memory (EEPROM or Flash) for program storage, and system memory for operating system functions. Memory sizes range from kilobytes to megabytes.