Siemens Simatic S7 Series System Manual

Program instructions
7.13 Program control
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
303
7.13.3
SCR (sequence control relay)
SCR (Sequence Control Relay) instructions provide a simple yet powerful state control
programming technique for a LAD, FBD, or STL program. Whenever an application consists
of a sequence of operations that must be performed repetitively, you can use SCRs to
structure the program so that it corresponds directly to your application. As a result, you can
program and debug the application quickly and easily.
WARNING
S bit usage in POUs
Do not use the same S bit in more than one POU. For example, if you use S0.1 in the main
program, do not use it in a subroutine.
Multiple POUs accessing the same S bit could result in unexpected process operation,
possibly resulting in death or severe personal injury.
Check your program to ensure that multiple POUs do not access the same S bit.
Note
SCR programming restrictions
•
You cannot jump into or out of an SCR segment; however, you can use Jump and Label
instructions to jump around SCR segments or to jump within an SCR segment.
•
You cannot use the END instruction in an SCR segment.

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.