Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 298)

Chapter 20
Math Instructions
20–22
This instruction can be used to solve linear equations of the form
Dest = (Rate/10000) x Source + Offse t
“Rate” is sometimes referred to as Slope.
When the SCL instruction is true, the value at the source address is
multiplied by the rate value. The rounded result is added to the offset value
and placed in the destination.
Example
SCL
SCALE
Source
N7:0
100
Rate [/10000] 25000
Offset 127
Dest N7:1
377
The source 100 is multiplied by
25000/10000 and added to 127.
The result 377 is placed in
the destination.
Important: In some cases, a mathematical overflow can occur before the
offset is added. The overflow sets minor error bit S:5/0. If this
bit is not reset in your ladder program before the end of the
scan, a major error will be declared.
Entering Parameters
The range of values for the following parameters is –32,768 to 32,767.
•
Source – This can be a program constant (decimal) or a word address.
•
Rate – This is the positive or negative value you enter divided by 10,000.
It can be a program constant (decimal) or a word address. The rate
parameter is limited to a range of –3.2768 to 3.2767.
•
Offset – This can be a program constant (decimal) or a word address.
•
Destination – This is a word address containing the linear calulation
(Rate/10000) x Source + Offset.
Using Arithmetic Status Bits
C reserved
V presence of an overflow at the destination is checked before and after the
offset value is applied. This bit is set if an overflow is detected; otherwise
reset. On overflow, minor error bit S:5/0 is also set and the value –32,768
or 32,767 is placed in the destination.
Z set when destination value is zero.
S set if the destination value is negative; otherwise reset.