Siemens Simatic S7 Series System Manual

Program instructions
7.13 Program control
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
305
S stack and logic stack interaction
The figure shows the S stack and the logic
stack and the effect of executing the
Load
SCR instruction.
Controlling program flow with SCR segments
The main program consists of instructions that execute sequentially once per scan of the
PLC. For many applications, it may be appropriate to logically divide the main program into a
series of operational steps that mirror steps within a controlled process (for example, a
series of machine operations).
One way to logically divide a program into multiple steps is to use SCR segments. SCR
segments can divide your program into a single stream of sequential steps, or into multiple
streams that can be active simultaneously. It is possible to have a single stream conditionally
diverge into multiple streams, and to have multiple streams conditionally re-converge into a
single stream.

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.