Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 User Manual
Page 102
Programming DH and DH+
Message Procedures
Chapter 6
6-11
Shift Operators
The scanner supports the following shift operators:
If you see:
It means the bit shifts:
<<
left
>>
right
The shift operators shift binary values a specified number of bit positions
to the left or right.
When a left arithmetic shift (<<) executes, zeros shift into the rightmost
bits of the expression. The leftmost bits shift out of the expression and are
lost, thus possibly changing the sign bit. The left bit shift operates in this
manner whether operating on 16 or 32 bit values.
PUMP = (PUMP << 1)
PUMP Value:
Bit Pattern (32Ćbits):
Decimal Value:
Before operation
100...00000101
-2147483643
After operation
000...00001010
10
In a similar manner, when a right bit shift (>>) is executed on a 16 bit
value in the data table, zeros shift into the leftmost bits of the expression.
The rightmost bits shift out of the expression and are lost. As shown in
this example, the sign can change when using the shift operators on 16-bit
values.
$N0:1 = ($N0:1 >> 1)
$N0:1 Value:
Bit Pattern (16Ćbits):
Decimal Value:
Before operation
10000011 00000000
-32000
After operation
01000001 10000000
16768
However, the right bit shift works differently when the operation is
performed on 32 bit values such as are created with user symbols, and also
values in the high order integer data table section. In this case, the leftmost
bit of the expression does not change.
If the leftmost bit is a:
Then:
1
a 1 is shifted in from the left.
0
a 0 is shifted in from the left.