Siemens Simatic S7-200 System Manual page 83

As shown in Figure 6-2, the S7-200 uses a logic stack to resolve the control logic. In these examples, "iv0"
to "iv7" identify the initial values of the logic stack, "nv" identifies a new value provided by the instruction,
and "S0" identifies the calculated value that is stored in the logic stack.
ALD
Before
AND the top
iv0
two stack
iv1
values
iv2
iv3
iv4
iv5
iv6
iv7
S0 = iv0 AND iv1 iv8
LPS Before
Logic Push
iv0
iv1
iv2
iv3
iv4
iv5
iv6
iv7
2
iv8
1
The value is unknown (it could be either a 0 or a 1).
2
After the execution of a Logic Push or a Load Stack instruction, value iv8 is lost.
Figure 6-2 Operations of the Logic Stack Instructions
Example: Logic Stack Instructions
OLD
After Before
OR the top two
S0 iv0
stack values
iv2 iv1
iv3 iv2
iv4 iv3
iv5 iv4
iv6 iv5
iv7 iv6
iv8 iv7
S0 = iv0 OR iv1
1
x iv8
LRD
After Before
Logic Read
iv0 iv0
iv0 iv1
iv1 iv2
iv2 iv3
iv3 iv4
iv4 iv5
iv5 iv6
iv6 iv7
iv7 iv8
Network 1
LD
LD
LD
A
OLD
ALD
=
Network 2
LD
LPS
LD
O
ALD
=
LRD
LD
O
ALD
=
LPP
A
=
S7-200 Instruction Set
LDS Before
After
Load Stack
S0 iv0
iv2 iv1
iv3 iv2
iv4 iv3
iv5 iv4
iv6 iv5
iv7 iv6
iv8 iv7
1 2
x iv8
LPP
After Before
Logic Pop
iv1 iv0
iv1 iv1
iv2 iv2
iv3 iv3
iv4 iv4
iv5 iv5
iv6 iv6
iv7 iv7
iv8 iv8
I0.0
I0.1
I2.0
I2.1
Q5.0
I0.0
I0.5
I0.6
Q7.0
I2.1
I1.3
Q6.0
I1.0
Q3.0
Chapter 6
After
iv3
iv0
iv1
iv2
iv3
iv4
iv5
iv6
iv7
After
iv1
6
iv2
iv3
iv4
iv5
iv6
iv7
iv8
1
x
71