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
6
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).
Positive and Negative Transition Instructions
The Positive Transition contact instruction (EU) allows power to flow for one scan for each off-to-on
transition. The Negative Transition contact instruction (ED) allows power to flow for one scan for each
on-to-off transition. For the Positive Transition instruction, detection of a 0-to-1 transition in the value on
the top of the stack sets the top of the stack value to 1; otherwise, it is set to 0. For a Negative Transition
instruction, detection of a 1-to-0 transition in the value on the top of the stack sets the top of the stack
value to 1; otherwise, it is set to 0.
For run-time editing (when you edit your program in RUN mode), you must enter a parameter for the
Positive Transition and Negative Transition instructions. Refer to Chapter 5 for more information about
editing in RUN mode.
Table 6-3
Inputs/Outputs
Bit
Bit (immediate)
66
Valid Operands for the Bit Logic Input Instructions
Data Type Operands
BOOL I, Q, V, M, SM, S, T, C, L, Power Flow
BOOL I