Programming options
5.3 Powerful and easy-to-use instruction set
Easy Book
58
Manual, 05/2009, A5E02486774-01
Like LAD, FBD is also a graphical programming language. The representation of the logic
is based on the graphical logic symbols used in Boolean algebra.
Mathematical functions and other complex
functions can be represented directly in
conjunction with the logic boxes. To create
the logic for complex operations, insert
parallel branches between the boxes.
5.3.2
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.
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.
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
Normally Closed
Contact
The Normally Open contact is closed (ON) when
the assigned bit value is equal to 1.
The Normally Closed contact is closed (ON)
when the assigned bit value is equal to 0.
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.
