# LD UDFB Guided Learning Q09: – Identify the implicit one shot in a state machine **URL:** \ **Category:** Automation and Control\ **Tags:** guided-learning\ **Created:** [June 21, 2025, 10:24pm UTC](https://forum.digikey.com/t/ld-udfb-guided-learning-q09-identify-the-implicit-one-shot-in-a-state-machine/56639 "2025-06-21T22:24:16Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![APDahlen](https://sea2.discourse-cdn.com/digikey/user_avatar/forum.digikey.com/apdahlen/32/40191_2.png) [@APDahlen](https://forum.digikey.com/u/APDahlen)\ **Post date:** [June 21, 2025, 10:24pm UTC](https://forum.digikey.com/t/ld-udfb-guided-learning-q09-identify-the-implicit-one-shot-in-a-state-machine/56639/1 "2025-06-21T22:24:16Z")
This article is part of a guided learning series on building and analyzing User-Defined Function Blocks (UDFBs). 📌 Canonical Article: [Building a User-Defined Function Block (UDFB) Using Siemens TIA Portal](https://forum.digikey.com/t/building-a-user-defined-function-block-udfb-using-siemens-tia-portal/56095) 📘 Learning Companion (Q&A): [Explore All Questions](https://forum.digikey.com/t/learning-companion-for-a-ladder-logic-based-user-defined-function-block/56388) You are reading: Question 9 ## Identify the implicit one shot in a state machine. ### Answer An implicit one shot occurs on every state transition. Consider the second branch of Figure 3 which activates on a fault when the motor starter fails to close within timClose. The timer output will be high for one and only one program cycle scan. The fact that we move to a new state ensures that the timer will reset on the next scan. With regard to a state machine, this is an important consideration when we want things to occur once, and only once, on the state transitions. As example is the S\_MOVE which is only activated for a single program scan. ✍ Article by Aaron Dahlen, LCDR USCG (Ret.), Application Engineer at DigiKey