Accessing Memory Areas - Siemens SIMATIC S7 System Manual

The following table shows the range of integer values that can be represented by the
different sizes of data.
Table 4- 3 Decimal and hexadecimal ranges for the different sizes of data
Representation Byte (B)
Unsigned Inte- 0 to 255
ger
16#00 to 16#FF
Signed Integer -128 to +127
16#80 to 16#7F
Not applicable
Real (IEEE 32-
bit Floating
Point)
Data in other memory areas (such as T, C, HC, and the accumulators) are accessed by
using an address format that includes an area identifier and a device number.
4.2.1

Accessing memory areas

I (process-image input)
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:
Table 4- 4
Bit:
Byte, Word, or Double Word:
Q (process-image output)
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:
Table 4- 5
Bit:
Byte, Word, or Double Word:
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Word (W)
0 to 65,535
16#0000 to 16#FFFF
-32,768 to +32,767
16#8000 to 16#7FFF
Not applicable
Absolute addressing for I memory
Absolute addressing for Q memory
Double Word (D)
0 to 4,294,967,295
16#00000000 to 16#FFFFFFFF
-2,147,483,648 to +2,147,483,647
16#8000 0000 to 16#7FFF FFFF
+1.175495E-38 to +3.402823E+38 (positive)
-1.175495E-38 to -3.402823E+38 (negative)
[byte address].[bit address]
I
[size][starting byte address]
I
[byte address].[bit address]
Q
[size][starting byte address]
Q
PLC concepts
4.2 Accessing data
I0.1
IB4,
IW7,
ID20
Q1.1
QB5, QW14,
QD28
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