# Xtend GPIO input voltage levels

**URL:** <https://forum.sierrawireless.com/t/xtend-gpio-input-voltage-levels/4587>\
**Category:** Legacy FX/FXT series\
**Created:** [July 28, 2010, 10:33am UTC](https://forum.sierrawireless.com/t/xtend-gpio-input-voltage-levels/4587 "2010-07-28T10:33:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![OOZ](https://avatars.discourse-cdn.com/v4/letter/o/db5fbb/32.png) [@OOZ](https://forum.sierrawireless.com/u/OOZ)\
**Post date:** [July 28, 2010, 10:33am UTC](https://forum.sierrawireless.com/t/xtend-gpio-input-voltage-levels/4587/1 "2010-07-28T10:33:39Z")

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Hey all,

I’m working with a Fastrack Xtend, using GPIOs 21 and 25 on the 10 pin power supply connector as inputs. The documentation doesn’t appear to make it particularly clear what the GPIO input voltages should be i.e. what constitutes logic 0 and logic 1 voltage levels, what the maximum input voltage level is, how the input voltage relates to Vref etc. Am I missing something in the documentation? Does anyone have any experience with this that they can share?

A related portion of Fastrack Xtend User Guide rev 2 follows:

> [@](#):
>
> 5.1.1.1. General Purpose Input/Output  
> The Fastrack Xtend has two external GPIO ports, GPIO21 and GPIO25; as well as a voltage reference line, Vref.  
> Vref sets the reference voltage of the input or output of the two GPIOs. Leaving it unconnected sets the GPIO level at 2.3V – 2.6V by default. It is recommended to connect to the required GPIOs’ output voltage (2.8V ~ 15V).  
> Refer to the following table for the pin description of the GPIOs.

Thanks.

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**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.sierrawireless.com/u/awneil)\
**Post date:** [August 2, 2010, 2:04pm UTC](https://forum.sierrawireless.com/t/xtend-gpio-input-voltage-levels/4587/2 "2010-08-02T14:04:51Z")

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> [@OOZ](#):
>
> Am I missing something in the documentation?

No, you’re not, I’m afraid - it really is rubbish! 😠

See: [Undocumented: Fastrack XTreme GPIO Current Ratings?](https://forum.sierrawireless.com/t/undocumented-fastrack-xtreme-gpio-current-ratings/4408/1)

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**Author:** ![OOZ](https://avatars.discourse-cdn.com/v4/letter/o/db5fbb/32.png) [@OOZ](https://forum.sierrawireless.com/u/OOZ)\
**Post date:** [August 6, 2010, 12:45pm UTC](https://forum.sierrawireless.com/t/xtend-gpio-input-voltage-levels/4587/3 "2010-08-06T12:45:17Z")

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I’ve read that post before while trawling through the forum, trying to make sense of it and feeling dumb for not finding these values 😐 . At least I’m not alone in this. But the Xtend is running well enough as it is, so I’m not going to loose too much sleep.

Thanks! 🙂