Watlow LogicPro - Manual (Page 158)

Chapter 10: Function Blocks LogicPro User’s Guide
142 Watlow Anafaze Doc.# 28002-00 Rev 3.00
Scan Time Counter (SCAN)
The Scan Time Counter (SCAN) function block, shown in
Figure 10.22, calculates the scan time system performance
while running a program.
SCAN calculates the scan time when the enable bit (EN) is
True. The current scan time (TIME) is displayed along with the
minimum value (MIN) and the maximum value (MAX) in
thousandths of a second. The output bit (Q) always assumes
the value of the enable bit; therefore, when the enable bit is
True, the output bit is also True.
The symbolic Variables for scan time, minimum, and
maximum must be of type Integer. These values change
dynamically as the program runs, as long as the enable bit is
True. When the enable bit becomes False, the Variables retain
their last value. The clear bit (CLR) resets and holds the
Variables at zero whenever it is True.
Figure 10.22 Scan Time Counter Function Block
Inputs
EN is the Scan Time Counter enable bit. A True condition of
this bit causes the scan time to be calculated. In a program
using Ladder logic, the value of EN is determined by the
Boolean evaluation of elements placed between the left power
rail and EN in the function block. In FBD programs, the value
of EN is determined by the Variable connected to EN. If no
contacts are placed on the rung before EN in a Ladder
Diagrams program, the value of EN is always True. In FBD,
all inputs must be connected to a Variable.
CLR is the Scan Time Counter clear bit. When this bit is True,
the values of TIME, MIN, and MAX are set and remain at zero.
In a Ladder Diagram program, the value of CLR is determined
by the Boolean evaluation of elements placed between the left
power rail and CLR in the function block. In FBD programs,
the value of CLR is determined by whatever is connected to
EN. If no contacts are placed on the rung before CLR in a