Siemens SIMATIC S7 System Manual page 303

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Natural logarithm (LN) and natural exponential (EXP) instructions

Non-fatal errors with ENO = 0

0006H Indirect address

SM1.1 Overflow

Input / outputs

Real (or floating-point) numbers are represented in the format described in the ANSI/IEEE 754-1985 standard (single-

precision). Refer to that standard for more information.

S7-200 SMART

System Manual, V2.3, 07/2017, A5E03822230-AF

The Natural Logarithm instruction (LN) performs the natural logarithm of the

value in IN and places the result in OUT.

The Natural Exponential instruction (EXP) performs the exponential operation of

e raised to the power of the value in IN and places the result in OUT.

LN (IN) = OUT

EXP (IN)= OUT

To obtain the base 10 logarithm from the natural logarithm: Divide the natural

logarithm by 2.302585 (approximately the natural logarithm of 10).

To raise any real number to the power of another real number, including frac-

tional exponents: Combine the Natural Exponential instruction with the Natural

Logarithm instruction. For example, to raise X to the Y power, use EXP (Y *

SM bits affected

SM1.0 Result of operation = zero

SM1.1 Overflow, illegal value generated during the operation, or illegal input

SM1.2 Negative result

ID, QD, VD, MD, SMD, SD, LD, AC, *VD, *LD, *AC, Constant

ID, QD, VD, MD, SMD, SD, LD, AC, *VD, *LD, *AC

Program instructions

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Simatic s7-200 smart