Siemens Simatic S7-200 System Manual page 133

Representation of Numbers
Table 7-1 shows the range of integer values that can be represented by the different sizes of
data.
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 number values are accessed
in double-word lengths.
Table 7-1 Data Size Designations and Associated Integer Ranges
Data Size Data Size
B (Byte): 8-bit value
W (Word): 16-bit value
D (Double word, Dword):
32-bit value
Addressing the Process-Image Input Register (I)
As described in Section 6.5, the CPU samples the physical input points at the beginning of
each scan cycle and writes these values to the process-image input register. You can access
the process-image input register in bits, bytes, words, or double words.
Format: Bit
Byte, Word, Double Word
Addressing the Process-Image Output Register (Q)
At the end of the scan cycle, the CPU copies the values stored in the process-image output
register to the physical output points. You can access the process-image output register in
bits, bytes, words, or double words.
Format: Bit
Byte, Word, Double Word
Addressing the Variable (V) Memory Area
You can use V memory to store intermediate results of operations being performed by the
control logic in your program. You can also use V memory to store other data pertaining to
your process or task. You can access the V memory area in bits, bytes, words, or double
words.
Format: Bit
Byte, Word, Double Word
Addressing the Bit Memory (M) Area
You can use the internal memory bits (M memory) as control relays to store the intermediate
status of an operation or other control information. While the name "bit memory area" implies
that this information is stored in bit-length units, you can access the bit memory area not only
in bits, but also in bytes, words, or double words.
Format: Bit
Byte, Word, Double Word
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
CPU Memory: Data Types and Addressing Modes
Unsigned Integer Range
Decimal Hexadecimal
0 to 255 0 to FF
0 to 65,535 0 to FFFF
0 to 0 to
4,294,967,295 FFFF FFFF
I [byte address].[bit address]
I [size][starting byte address] IB4
Q [byte address].[bit address]
Q [size][starting byte address] QB5
V [byte address].[bit address]
V [size][starting byte address] VW100
M [byte address].[bit address]
M [size][starting byte address] MD20
Signed Integer Range
Decimal Hexadecimal
-128 to 127 80 to 7F
-32,768 to 32,767 8000 to 7FFF
-2,147,483,648 to 8000 0000 to
2,147,483,647 7FFF FFFF
I0.1
Q1.1
V10.2
M26.7
7-3