Siemens Simatic S7 Series System Manual

PLC concepts
4.2 Accessing data
S7-200 SMART
68 System Manual, 09/2015, A5E03822230-AC
S (sequence control relay)
S bits are associated with SCRs, which you can use to organize machine or steps into
equivalent program segments. SCRs allow logical segmentation of the control program. You
can access the S memory as bits, bytes, words, or double words.
Table 4- 16 Absolute addressing of S memory
Bit: S [byte address].[bit address] S3.1
Byte, Word, or Double Word: S [size][starting byte address] SB4,
SW7,
SD14
4.2.2
Format for Real numbers
Real (or floating-point) numbers are represented as 32-bit, single-precision numbers, whose
format is described in the ANSI/IEEE 754-1985 standard. Real numbers are accessed in
double-word lengths.
Figure 4-5 Format of a Real number
Note
Floating
-point numbers are accurate up to 6 decimal places. Therefore, you can specify a
maximum of 6 decimal places when entering a floating
-point constant.
Calculations that involve a long series of values including very large and very small numbers
can produce inaccurate results. This can oc
cur if the numbers differ by 10 to the power of x ,
where
x > 6. For example: 100 000 000 + 1 = 100 000 000
4.2.3
Format for strings
A string is a sequence of characters, with each character being stored as a byte. The first
byte of the string defines the length of the string, which is the number of characters. The
following figure shows the format for a string. A string can have a length of 0 to 254
characters, plus the length byte, so the maximum length for a string is 255 bytes. A string
constant is limited to 126 bytes.
Figure 4-6 Format for strings

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.