Siemens Simatic S7 Series System Manual

Program instructions
7.1 Bit logic
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
157
7.1.6
Positive and negative transition detectors
LAD
FBD
STL
Description
EU
ED
The positive transition contact instruction (Edge Up) allows power to
flow for one scan for each OFF-to-ON transition.
The negative transition contact instruction (Edge Down) allows power
to flow for one scan for each ON-to-OFF transition.
S7-200 SMART CPUs support a combined total (positive and nega-
tive) of 1024 edge detector instructions in your program.
LAD
: Positive and negative transition instructions are represented by
contacts.
FBD
: The transition instructions are represented by the P and N box-
es.
STL
: The positive transition is detected by the EU (Edge Up) instruc-
tion. Upon detection of a 0-to-1 transition in the value on the top of the
stack, the top of the stack value is set to 1; otherwise, it is set to 0.
The negative transition is detected by the ED (Edge Down) instruc-
tion. Upon detection of a 1-to-0 transition in the value on the top of the
stack, the top of the stack value is set to 1; otherwise, it is set to 0.
Input / output
Data type
Operand
IN (FBD)
BOOL
I, Q, V, M, SM, S, T, C, L, Logic flow
OUT (FBD)
BOOL
I, Q, V, M, SM, S, T, C, L, Logic flow
Note
Because the Positive Transition and Negative Transition instructions require an on
-to-off or
an
off-to-on transition, you cannot detect an edge-up or edge-down transition on the first
scan. During the first scan, the CPU saves the initial input state in a memory bit. On
subsequent scans, these instructions compare the current state and the state of the memory
bit, to detect a transition.
See also
Bit logic input examples (Page 162)

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.