Assigning A Constant Value For Instructions; Addressing The Local And Expansion I/O - Siemens SIMATIC S7 System Manual

4.2.4

Assigning a constant value for instructions

You can use a constant value in many of the programming instructions. Constants can be
bytes, words, or double words. The CPU stores all constants as binary numbers, which can
then be represented in decimal, hexadecimal, ASCII, or real number (floating point) formats.
Table 4- 17
Representation
Decimal
Hexadecimal
Binary
ASCII
Real
String
Note
The CPU does not support "data typing" or data checking (such as specifying that the
constant is stored as an integer, a signed integer, or a double integer). For example, an Add
instruction can use the value in VW100 as a signed integer value, while an Exclusive Or
instruction can use the same value in VW100 as an unsigned binary value.
4.2.5

Addressing the local and expansion I/O

The local I/O provided by the CPU provides a fixed set of I/O addresses. You can add I/O
points by connecting expansion I/O modules to the right side of the CPU or by installing a
signal board. The addresses of the points of the module are determined by the type of I/O
and the position of the module in the chain. For example, an output module does not affect
the addresses of the points on an input module, and vice versa. Likewise, analog modules
do not affect the addressing of digital modules, and vice versa.
Note
Process image register space for digital I/O is always reserved in increments of eight bits
(one byte). If a module does not provide a physical point for each bit of each reserved byte,
these unused bits cannot be assigned to subsequent modules in the I/O chain. For input
modules, the unused bits are set to zero with each input update cycle.
Analog I/O points are always allocated in increments of two points. If a module does not
provide physical I/O for each of these points, these I/O points are lost and are not available
for assignment to subsequent modules in the I/O chain.
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Representation of constant values
Format
[decimal value]
16#[hexadecimal value]
2#[binary number]
'[ASCII text]'
ANSI/IEEE 754-1985
"[stringtext]"
Sample
20047
16#4E4F
2#1010_0101_1010_0101
'ABCD'
+1.175495E-38 (positive)
-1.175495E-38 (negative)
"ABCDE"
PLC concepts
4.2 Accessing data
83