Siemens Simatic S7 Series System Manual

Program instructions
7.4 Compare
S7-200 SMART
196 System Manual, 09/2015, A5E03822230-AC
7.4.2
Compare character strings
The compare string instructions can compare two ASCII character strings.
For
LAD
and
FBD:
When the comparison is TRUE, the compare instruction turns ON the
contact (LAD), or output (FBD).
For
STL
: When the comparison is TRUE, the compare instruction loads, ANDs, or ORs a 1
with the value on the top of the logic stack.
Comparisons can be made between two variables, or between a constant and a variable. If a
constant is used in a comparison, then it must be the top parameter (LAD contact / FBD box)
or the first parameter (STL).
In the program editor, a constant string parameter assignment must begin and end with a
double quote character. The maximum length of a constant string entry is 126 characters
(bytes).
In contrast, a variable string is referenced by the byte address of the initial length byte with
the character bytes stored the next byte addresses. A variable string has a maximum length
of 254 characters (bytes) and can be initialized in the data block editor (with beginning and
ending double quote character).
LAD contact
FBD box
STL
Description
LDS= IN1, IN2
OS= IN1, IN2
AS= IN1, IN2
Compare two character strings of STRING data type:
The result is TRUE, if string IN1
equals
string IN2.
LDS<> IN1, IN2
OS<> IN1, IN2
AS<> IN1, IN2
Compare two character strings of STRING data type:
The result is TRUE, if string IN1
does not equal
string IN2.

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.