Providing The Basic Instructions You Expect - Siemens SIMATIC S7-1200 Manual
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- Function manual (527 pages) ,
- Manual (364 pages) ,
- System manual (338 pages)
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Programming concepts made easy
5.3 Easy to use the powerful programming languages
5.3.1
Providing the basic instructions you expect
Bit logic instructions
The basis of bit logic instruction is contacts and coils. Contacts read the status of a bit, while
the coils write the status of the operation to a bit.
If you use a coil with the same address in more than one program segment, the result of the
last calculation in the user program determines the status of the value for that address.
Normally Open
Contact
The basic structure of a bit logic operation is either AND logic or OR logic. Contacts
connected in series create AND logic networks. Contacts connected in parallel create OR
logic networks.
You can connect contacts to other contacts and create your own combination logic. If the
input bit you specify uses memory identifier I (input) or Q (output), then the bit value is read
from the process-image register. The physical contact signals in your control process are
wired to input terminals on the PLC. The CPU scans the wired input signals and updates the
corresponding state values in the process-image input register.
You can specify an immediate read of a physical input using ":P" following the tag for an
input (such as "Motor_Start:P" or "I3.4:P"). For an immediate read, the bit data values are
read directly from the physical input instead of the process image. An immediate read does
not update the process image.
Output coil
● If there is power flow through an output coil, then the output bit is set to 1.
● If there is no power flow through an output coil, then the output coil bit is set to 0.
● If there is power flow through an inverted output coil, then the output bit is set to 0.
● If there is no power flow through an inverted output coil, then the output bit is set to 1.
56
Normally Closed
The Normally Open contact is closed (ON) when
Contact
the assigned bit value is equal to 1.
The Normally Closed contact is closed (ON)
when the assigned bit value is equal to 0.
Inverted output coil
Contacts test the binary status of
the bit, with the result being
"power flow" if on (1) or "no power
flow" if off (0).
The state of the coil reflects the
status of the preceding logic.
Manual, 11/2009, A5E02486774-01
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