Automationdirect.com DL05 - Reset Watch Dog Timer (RSTWT)

Standard
RLL Instructions
5–95
Standard RLL Instructions
CPU Control Instructions
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.
RSTWT
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.
DirectSOFT
Handheld Programmer Keystrokes
RSTWT
SHFT
ORN
R
RST
S
MLR
T
ANDN
W
MLR
T
ENT
Reset Watch Dog
Timer
(RSTWT)