AutomationDirect DL205 User Manual

DL205 User Manual, 4th Edition, Rev. D
3-29
Chapter 3: CPU Specifications and Operations
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CPU Scan Time Considerations
The scan time covers all the cyclical tasks
that the operating system performs. You
can use DirectSOFT or the Handheld
Programmer to display the minimum,
maximum, and current scan times that have
occurred since the previous Program Mode
to Run Mode transition. This information
can be very important when evaluating
system performance.
As shown previously, there are several
segments that make up the scan cycle. Each
of these segments requires a certain amount
of time to complete. Of all the segments,
the only one you really have the most control
over is the amount of time it takes to execute
the application program. This is because
different instructions take different amounts
of time to execute. So, if you think you need
a faster scan, then you can try to choose
faster instructions.
Your choice of I/O modules and system
configuration, such as expansion or remote
I/O, can also affect the scan time; however,
the application usually dictates them.
For example, if you need to count pulses at
high rates of speed, then you will probably
have to use a High-Speed Counter module.
Also, if you have I/O points that need to be
located several hundred feet from the CPU,
then you need remote I/O because it is much
faster and cheaper to install a single remote
I/O cable than it is to run all those signal
wires for each individual I/O point. The
following paragraphs provide some general
information on how much time some of the
segments can require.
YES
Power up
Initialize hardware
Check I/O module
config. and verify
Initialize various memory
based on retentive
configuration
Update input
Read input data from
Specialty and Remote I/O
Service peripheral
PGM
Mode?
RUN
Execute ladder program
Update output
Write output data to
Specialty and Remote I/O
Do diagnostics
OK
NO
NO
Fatal error
Force CPU into
PGM mode
OK?
Report the error, set flag,
register, turn on LED
YES
CPU Bus Communication
Update Clock / Calendar
PID Equations (DL250-1/DL260)

AutomationDirect DL205 Specifications

General

Brand	AutomationDirect
Model	DL205
Category	Controller
Language	English