Bit Logic Instructions; Contacts - Siemens SIMATIC S7-200 System Manual

S7-200 Programmable Controller System Manual

Bit Logic Instructions

Contacts

Standard Contacts
The Normally Open contact instructions (LD, A, and O) and
Normally Closed contact instructions (LDN, AN, ON) obtain
the referenced value from the memory or from the
process-image register. The standard contact instructions
obtain the referenced value from the memory (or
process-image register if the data type is I or Q).
The Normally Open contact is closed (on) when the bit is
equal to 1, and the Normally Closed contact is closed (on)
when the bit is equal to 0. In FBD, inputs to both the And
and Or boxes can be expanded to a maximum of 32 inputs.
In STL, the Normally Open instructions Load, AND, or OR
the bit value of the address bit to the top of the stack, and
the Normally Closed instructions Load, AND, or OR the
logical NOT of the bit value to the top of the stack.
Immediate Contacts
An immediate contact does not rely on the S7-200 scan
cycle to update; it updates immediately. The Normally Open
Immediate contact instructions (LDI, AI, and OI) and
Normally Closed Immediate contact instructions (LDNI, ANI,
and ONI) obtain the physical input value when the
instruction is executed, but the process-image register is
not updated.
The Normally Open Immediate contact is closed (on) when
the physical input point (bit) is 1, and the Normally Closed
Immediate contact is closed (on) when the physical input
point (bit) is 0. The Normally Open instructions immediately
Load, AND, or OR the physical input value to the top of the
stack, and the Normally Closed instructions immediately
Load, AND, or OR the logical NOT of the value of the
physical input point to the top of the stack.
NOT Instruction
The Not instruction (NOT) changes the state of power flow
input (that is, it changes the value on the top of the stack
from 0 to 1 or from 1 to 0).
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