Publication 1766-RM001A-EN-P - October 2008
Math Instructions
229
LOG - Base 10 Logarithm
Instruction Type: output
LN Instruction Operation
Inputs
Conditions
Output
Source Type
Destination
Type
S:2/14
S:0/3-0
S, Z, V, C
S:5/0
Destination
W,DW, F
F
X
Source > 1
0,0,0,0
L
Ln(Source)
W,DW, F
F
X
Source = 1
1,0,0,0
L
0
W,DW, F
F
X
0 < Source < 1
1,0,0,0
L
Ln(Source)
W,DW, F
W, DW
X
Source >= Sqrt(e)
0,0,0,0
L
Rnd(Ln(Source))
W,DW, F
W, DW
X
1/Sqrt(e) < Source < Sqrt(e)
1,0,0,0
L
0
W,DW, F
W, DW
X
0 < Source <= 1/Sqrt(e)
1,0,0,0
L
Rnd(Ln(Source))
(1)
+DNRM
F
X
X
1,0,1,0
1
-INF
(1)
(2)
+DNRM
W
X
X
1,0,1,0
1
-32768
(1)
(2)
+DNRM
DW
X
X
1,0,1,0
1
-2147483648
(1)
(3)
W,DW, F
F
X
Source <= 0 (including -DNRM)
0,0,1,0
1
0x7FFFFFFF
(2)
W,DW, F
F
X
Source = +INF
0,0,1,0
1
+INF
(3)
X
F
X
Source is NAN or -INF
0,0,1,0
1
0x7FFFFFFF
(4)
X
W
X
Source is NAN or INF
0,0,1,0
1
32767
(4)
X
DW
X
Source is NAN or INF
0,0,1,0
1
2147483647
(1) All denormalized inputs shall be treated as plus zero.
(2) If the Destination is word or double-word and an overflow occurs (except source is NAN or INF), destination is -32768 for Word and -2147483648 for Double Word.
(3) If the Destination is floating point, all overflows (INF) shall produce NAN (0x7FFFFFFF).
(4) If Destination is an integer and the Source is NAN or infinity (+INF or -INF), a saturated result (32767 for Word and 2147483647 for Double Word) shall be stored.
AB
S
Log Base 10
S
ource
N7
:
0
0<
Dest
N7
:
1
0<
LOG
Execution Time for the LOG Instruction
Controller
Data Size
When Rung Is:
True
False
MicroLogix 1400
word
112.7110 µs
0.7686 µs
long word
19.8070 µs
0.7694 µs
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