DL06 Micro PLC User Manual, 3rd Edition, Rev. E
5-174
Chapter 5: Standard RLL Instructions
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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
Direct SOFT 32
Handheld Programmer Keystrokes
RSTWT
SHFT
ORN
R
RST
S
MLR
T
ANDN
W
MLR
T
ENT
DS
Used
HPP Used
Direct
SOFT
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.
