Siemens SIMATIC S7-200 - Here Are the Bits

Quick review
1.2 Here are the Bits
Getting Started - Advanced
8 Training Documents, 09/2007, A5E01469795B
1.2 Here are the Bits
The smallest unit to be processed is the bit! The bit can assume two states:
● "1" meaning "bit set" or state is "true"
● "0" meaning "bit not set " or state is "false"
In a method familiar to you, the two binary states "1" and "0" can be represented as electrical
circuits, that is, they can be represented by current flow (1) and no current flow (0).
A closed switch:
Current flows so bit state = "1"
"1" = "true" =
Current flows
and an open switch:
No current flows so bit state = "0".
"0" = "false" =
No current
flows
From here it requires only a short step
to the representation of logic operations
as circuits, e.g. series connection of
two contacts.
The AND operation of inputs I0.0 and
I0.1 is represented as shown on the
right.
,
,
AND
operation
This is represented as follows in LAD:
,
,
Finally, a small convention:
The following applies for positive logic:
24V = high-level = "1" and
0V = low-level = "0".
positive logic
The following applies for negative logic:
0V = low-level = "1"
24V = high-level = "0".
negative logic