Control Techniques UD70, User Manual

Page: 39 / 154

UD70
Issue code: 70nu2
DPL programming 4-17
Integer division
When using integer division, accuracy may be lost in the result, as shown in
the following expression:
If #1.21 is equal to 5
Then we have the following:
a = 4.5 * (#1.21 /4)
= 4.5 * (5 /4)
= 4.5 * 1
= 4.5
The DPL compiler uses an integer divide, converts the result to a
floating-point value and uses a floating-point multiply.
To preserve accuracy, one of the arguments can be converted to a
floating-point variable, as follows:
a = 4.5 * (#1.21 / FLOAT(4) )
= 4.5 * (5 / FLOAT(4) )
= 4.5 * 1.25
= 5.625
See
FLOAT
instruction in Chapter 7 Reference.
PRINT instruction
Do not over-use the
PRINT
instruction. (See PRINT instruction in Chapter 7
Reference). It is preferable to use the Watch Watch window in the DPL Toolkit to
monitor variables (see Chapter 5 DPL Toolkit).
Use the
PRINT
instruction only in the
BACKGROUND
task. If the
PRINT
instruction is included in the
SPEED, CLOCK
or
ENCODER
tasks, the
PRINT
instruction may have insufficient time to be executed. Text waiting for
printing may not then be printed.
BACKGROUND task
Place as much of the program as possible in the
BACKGROUND
task rather
than in the
SPEED, CLOCK, ENCODER
or other real-time tasks. Since the real-
time tasks are on a fixed timebase, the processing must be completed in this
time. The
BACKGROUND
task does not have this restriction.