DL06 Micro PLC User Manual, 3rd Edition, Rev. E
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Chapter 3: CPU Specifications and Operation
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Diagnostics
During this part of the scan, the CPU performs all system diagnostics and other tasks such as
calculating the
scan time
and resetting the
watchdog time
r. There are many different error
conditions that are automatically detected and reported by the DL06 PLCs. Appendix B
contains a listing of the various error codes.
Probably one of the more important things that occurs during this segment is the
scan tim
e
calculation and watchdog timer control
. The DL06 CPU has a
watchdog timer
that stores
the maximum time allowed for the CPU to complete the solve application segment of the
scan cycle. If this time is exceeded, the CPU will enter the Program Mode and turn off all
outputs. The default value set from the factory is 200 ms. An error is automatically reported.
For example, the Handheld Programmer would display the following message
“E003 S/W
TIMEOUT”
when the scan overrun occurs.
You can use AUX 53 to view the minimum, maximum, and current scan time. Use AUX 55 to
increase or decrease the watchdog timer value.
I/O Response Time
Is Timing Important for Your Application?
I/O response time
is the amount of time required for the control system to sense a change in an
input point and update a corresponding output point. In the majority of applications, the CPU
performs this task in such a short period of time that you may never have to concern yourself
with the aspects of system timing. However, some applications do require extremely fast update
times. In these cases, you may need to know how to determine the amount of time spent during
the various segments of operation.
There are four things that can affect the I/O response time.
• The point in the scan cycle when the field input changes states
• Input Off to On delay time
• CPU scan time
• Output Off to On delay time
The next paragraphs show how these items interact to affect the response time.
