topic Kinetis GPIO Input Transition Time in Kinetis Microcontrollers

Kinetis GPIO Input Transition Time

gcary — Thu, 08 Jan 2015 02:41:43 GMT

What is the Kinetis GPIO timing requirement for the input transition time? It doesn't look like the inputs can be configured as Schmitt Triggers, and I don't see any mention of how slow the inputs can transition. Will it be a problem if they hover at VDD/2? In particular I am interested in the K2 Kinetis devices, but I'd like to know what the answer is for all Kinetis devices.

Thanks,

Greg

Re: Kinetis GPIO Input Transition Time

egoodii — Thu, 08 Jan 2015 15:05:51 GMT

I see Kinetis K20 datasheet spec Vhys as 0.06*Vdd. Of course digital inputs >Vil and <Vih incur additional input-stage current.

Re: Kinetis GPIO Input Transition Time

apanecatl — Thu, 08 Jan 2015 19:53:31 GMT

Well in the case of a microcontroller, the GPIO's philosophy is to drive or detect a digital signal always faster, our Kinetis K microcontroller's GPIO module detection window is depicted as:

As you can see these figures state a minimum time window/signal width during which an incoming signal could be detected. Of course an incoming signal can be significantly slower and it will be detected as soon as it crosses the threshold voltage level regardless of the time the signal takes to do so:

Re: Kinetis GPIO Input Transition Time

gcary — Thu, 08 Jan 2015 20:32:54 GMT

Thanks to both of you for answering my question. So the inputs have about 200 mV of hysteresis at 3.3V VDD. That is more than enough to protect the input from damage if the voltage is hovering near the threshold.

Regards,

Greg