# \[WP7605\]\[SW\] How to indicate the periodic signal, in order to use external Window WDT

**URL:** <https://forum.legato.io/t/wp7605-sw-how-to-indicate-the-periodic-signal-in-order-to-use-external-window-wdt/5087>\
**Category:** Legato Linux distribution (Yocto project)\
**Created:** [March 18, 2020, 11:52pm UTC](https://forum.legato.io/t/wp7605-sw-how-to-indicate-the-periodic-signal-in-order-to-use-external-window-wdt/5087 "2020-03-18T23:52:32Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![HIROKI11976](https://avatars.discourse-cdn.com/v4/letter/h/a9adbd/32.png) [@HIROKI11976](https://forum.legato.io/u/HIROKI11976)\
**Post date:** [March 18, 2020, 11:52pm UTC](https://forum.legato.io/t/wp7605-sw-how-to-indicate-the-periodic-signal-in-order-to-use-external-window-wdt/5087/1 "2020-03-18T23:52:33Z")

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Back Ground:  
WP7605 does not support HW WDT, so I consider to use external Window WDT IC in the case of runaway the legato or WP7605.  
In this case, Window WDT needs the periodic pulse from WP76xx, in order to notify keep-alive.

Question:  
Could you tell me the way how to indicate the periodic pulse to external IC?

BTW, we don’t use legato application, we only use native Linux application.  
So it is better for us to control it by using kernel command. (such as ioctrl())

Best Regards,

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**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/jyijyi/32/822_2.png) [@jyijyi](https://forum.legato.io/u/jyijyi)\
**Post date:** [March 19, 2020, 2:05am UTC](https://forum.legato.io/t/wp7605-sw-how-to-indicate-the-periodic-signal-in-order-to-use-external-window-wdt/5087/2 "2020-03-19T02:05:21Z")

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please see the attached doc on generating PWM signal.[Example\_on\_simulating\_pulse\_width\_modulation(PWM).docx](https://forum.legato.io/uploads/short-url/qXMGFOqg36U5uZ7TN5w7clqQ7HA.docx) (77.5 KB)