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[Need help] PIC32 not recognizing 2.78V as logic 1

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Full Member level 6
May 16, 2008
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Dear friends, i am new to PIC32 & i'm using PIC32MX564F128H microcontroller. Operating voltage of uC is 3.3V. I need to interface a GSM module with PIC32 microcontroller. The STATUS pin is delivering output voltage of 2.78V, but the microcontroller not recognizing this voltage as logic 1.
If i connect a 3.3V supply directly it sense it as a logic 1.

I am using RG3 pin for this connection & it is a schemitt trigger input. As per the datasheet it should sense the voltage of 0.8*VDD=2.64V as logic 1. But i am giving 2.78V & the uC not able to sense this why?
Please ask me is there any other parameter you need to know...

Thanks & Regards

I try to operate the uC using 3.0v. now i can sense 0.8*VDD=2.4V, but even for 2.78V i can not able to measure it as logic 1...:-(
Help me please...


Assume some of the Pic32 pins are straight digital inputs without the ST, does it work ok on one of them.

If not you could try a weak pull up of 47k or 100k; does the gsm datasheet say one is needed ? 5k or 10k is more common if specified.

Might be obvious, but you have got the pics ground and the gsm modules ground connected togther ?

Dear friend,
thanks for the reply. The pin i am using is not a direct digital input pin & its a ST buffer pin. I dont know what is the exact different between direct digital input Vs ST input but both are having minimum sensing voltage of 0.8V*VDD.
I don't get information about the internal STATUS pin pull up but i hope there should be a internal pullup resistor, because i can able to measure stable 2.78v output from the module. The application diagram doesn't have any external pullup resistors.
But as per your advise i will connect a pull up and will test again. thank you...

Another information i can sense the STATUS pin voltage while using PIC18 series microcontroller...:cry:



  • pic32 electrical.png
    pic32 electrical.png
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Have not used the Pic32s but as you say it works on a pic18 then it would seem likely you have not configured your port correctly.

Seems pic32 ports are a major job to set up / understand - have you seen this section of the Pic32 Reference manual ?
**broken link removed**
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