DL205 User Manual, 4th Edition, Rev. B
5–178
Chapter 5: Standard RLL Instructions - CPU Control
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Reset Watch Dog Timer (RSTWT)
The Reset Watch Dog Timer instruction resets the CPU scan
timer. The default setting for the watch dog timer is 200ms.
Scan times very seldom exceed 200ms, but it is possible.
For/next loops, subroutines, interrupt routines, and table
instructions can be programmed such that the scan becomes
longer than 200ms. When instructions are used in a manner
that could exceed the watch dog timer setting, this instruction
can be used to reset the timer.
A software timeout error (E003) will occur and the CPU will enter the program mode if the
scan time exceeds the watch dog timer setting. Placement of the RSTWT instruction in the
program is very important. The instruction has to be executed before the scan time exceeds
the watch dog timer’s setting.
If the scan time is consistently longer than the watch dog timer’s setting, the timeout value
may be permanently increased from the default value of 200ms by AUX 55 on the HPP or
the appropriate auxiliary function in your programming package. This eliminates the need for
the RSTWT instruction.
In the following example the CPU scan timer will be reset to 0 when the RSTWT instruction
is executed. See the For/Next instruction for a detailed example.
RSTWT
230
2
4
0
2
5
0
-1
2
6
0
ý
þ
þ
þ
Direct
SOFT
Handheld Programmer Keystrokes
RSTWT
SHFT
ORN
R
RST
S
MLR
T
ANDN
W
MLR
T
ENT
DS
Used
HPP Used
