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allenhuffman
Joined: 17 Jun 2019
Posts: 644
Location: Des Moines, Iowa, USA
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| can input() change the output of a PIN? |
 Posted: Fri Nov 07, 2025 7:21 am |
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We have a PIC24-based board that uses an output pin to toggle a synthesizer chip between internal mode (where it generates the RF signal) or external mode (where it takes a signal from an external source).
We toggle this mode like this:
| Code: | void setRFInternal(void)
{
powerUpFrequency (); // Power up the ADF device.
output_low(RF_IN_SEL);
}
void setRFExternal(void)
{
powerDownFrequency (); // Power down the ADF device.
output_high(RF_IN_SEL);
}
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I just enabled a new message in the firmware to show the status of this, and the code that was there (written years ago, never used) is this:
| Code: | bool RFIsInternal(void)
{
return (input(RF_IN_SEL) == 0);
}
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We now have a new weird problem where the mode switches back, and I am wondering if this input() is doing it. It would change the pin to an input() to read it, and never be changed back to an output.
Am I on the right track? This should really use input_state() to read the pin without changing it?
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ?
Using: 24FJ256GA106, 24EP256GP202 and 24FJ64GA002. |
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temtronic
Joined: 01 Jul 2010
Posts: 9590
Location: Greensville,Ontario
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| Posted: Fri Nov 07, 2025 8:06 am |
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pretty sure you're on the right track
input() will change pin to an input
input_state() should just read whether pin is a 1 or 0
cut small test program with those two , compile and then dump the listing to see what is actually happening !!
ever since I switched ISPs my 'engineering' PC hasn't been the same....another of life's mysteries... |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19970
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| Posted: Fri Nov 07, 2025 8:17 am |
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and of course, think how the pin is biased when it is set to input.
Should you perhaps have a pull up on it, so if floating it will go high, and
the input being low will mean it is being driven?. (or a pull down depending
on what is expected and generated). |
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