Due bug: Cannot use pin as digital after analogRead #2198
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@trickedj I'll open a pull request for this in order to fix it |
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here the pull request |
agdl
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Dec 5, 2014
If an analog input is used and during the sketch modified in a digitalOutput
the pinMode(AX, OUTPUT) isn't sensed because of this line of codes:
wiring_analog.c line 135
// Enable the corresponding channel
if (ulChannel != latestSelectedChannel) {
adc_enable_channel( ADC, ulChannel );
if ( latestSelectedChannel != (uint32_t)-1 )
adc_disable_channel( ADC, latestSelectedChannel );
latestSelectedChannel = ulChannel;
The channel is infact enabled only if different from the previous one because
of speed problems.
With my patch:
when pinMode(PIN, OUTPUT) is declared a control about if the pin
is an analog one is done and if so the ADC is released
when pinMode(PIN, INPUT) is declared a control is as well done in order to
enable the ADC.
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I am not sure that calling "adc_enable_channel" for the input mode is |
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I wasn't sure too, but i tested it and it works. That if that checks if the channel is changed is a problem. |
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I've added some thoughts and code on https://groups.google.com/a/arduino.cc/forum/#!topic/developers/IdhTIT0V5GY , |
facchinm
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Mar 27, 2015
to avoid the bug arduino#2198 simply reconfigure the pin -> no additional overhead if pinMode configuration is performed at the beginning of the sketch, 4 to 25% overhead on all analogRead() due to the additional check
facchinm
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Mar 27, 2015
to avoid the bug arduino#2198 simply reconfigure the pin -> no additional overhead if pinMode configuration is performed at the beginning of the sketch, 4 to 25% overhead on all analogRead() due to the additional check
facchinm
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Jul 14, 2015
to avoid the bug arduino#2198 simply reconfigure the pin -> no additional overhead if pinMode configuration is performed at the beginning of the sketch, 4 to 25% overhead on all analogRead() due to the additional check
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Solved by #3524 |
ollie1400
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May 2, 2022
to avoid the bug arduino#2198 simply reconfigure the pin -> no additional overhead if pinMode configuration is performed at the beginning of the sketch, 4 to 25% overhead on all analogRead() due to the additional check
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Once a pin has been used by analogRead it cannot be returned to digital use with pinMode(xxxx, OUTPUT) because analogRead only frees up the pin when another channel is read. pinMode needs to check if the pin is currently selected for the ADC and if so free it up.
A work around is to free up the pin by selecting a spare with analogRead
I discovered this while porting (from a Uno to Due) a TFT+touchpanel screen which shares digital TFT functions with raw touchpanel resistors.
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