Siemens SIMATIC S7 System Manual page 232

Program instructions
7.4 Compare
Note
The following conditions cause a non-fatal error, set power flow to OFF (ENO bit = 0), and
use value 0 as the result of the comparison
• Illegal indirect address is encountered (any compare instruction)
• Illegal real number (for example, NaN) is encountered for compare real instruction
To prevent these conditions from occurring, ensure that you properly initialize pointers and
values that contain real numbers before executing compare instructions that use these
values.
Compare instructions are executed regardless of the state of power flow.
Input / output Data type
IN1, IN2 BYTE
INT
DINT
REAL
OUT BOOL
232
Operand
IB, QB, VB, MB, SMB, SB, LB, AC, *VD, *LD, *AC, Constant
IW, QW, VW, MW, SMW, SW, T, C, LW, AC, AIW, *VD, *LD, *AC, Constant
ID, QD, VD, MD, SMD, SD, LD, AC, HC, *VD, *LD, *AC, Constant
ID, QD, VD, MD, SMD, SD, LD, AC, *VD, *LD, *AC, Constant
LAD: Power flow
FBD: I, Q, V, M, SM, S, T, C, L, Logic Flow
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART