Arduino Forum

Development => Other Hardware Development => Topic started by: Gates on Mar 07, 2013, 09:08 am

Title: Pin A6 and A7
Post by: Gates on Mar 07, 2013, 09:08 am
I have been looking at the schematic for the Arduino etherten board. I was wondering if these pins can be used or, if they are already being used. These pins are located near the SD card slot.
Title: Re: Pin A6 and A7
Post by: westfw on Mar 07, 2013, 12:05 pm
They can do analog input only...
Title: Re: Pin A6 and A7
Post by: Gates on Mar 07, 2013, 12:18 pm
I want to know if they are reserved for any reason. If they are reserved I would like to know what processes call of them to be open analog pins.
Title: Re: Pin A6 and A7
Post by: Gates on Mar 07, 2013, 04:04 pm
Found it....
"Just a reminder that this TQFP package (AU) has 2 more ADC's than the DIP package (P), but (Arduino) A6 and A7 are only analog inputs, they cannot be used for outputs - nor do they have any pull-ups on them."
Title: Re: Pin A6 and A7
Post by: Nick_Pyner on Mar 07, 2013, 11:06 pm
OK, so I now understand that my Etherten almost looks, walks and quacks like a Uno - but not quite. There is this functional difference, and it's all down to the different chip package. Is there any known instance of these pins being used? Freetronics are clearly not that serious about them.
Title: Re: Pin A6 and A7
Post by: JChristensen on Mar 07, 2013, 11:46 pm
I have a project in the pipe that will use them to monitor battery voltage. A few weeks off yet.
Title: Re: Pin A6 and A7
Post by: WinstonP on Mar 08, 2013, 01:01 am
may be useful for an analog keyboard or onboard temperature probe.
Title: Re: Pin A6 and A7
Post by: westfw on Mar 08, 2013, 02:56 am
A6 and A7 were also available on the Arduino Mini and Arduino Nano (and presumably some of the other SMT-chip based third party boards.)  But using them is not compatible with the "popular" Arduino boards (Uno and its predecessors), and actually using them has never caught on.
Title: Re: Pin A6 and A7
Post by: Gates on Mar 08, 2013, 06:50 am
I am planning on making a Header file to include these pins ("A6,A7").  I was reading the schematic and found them open. 1K resistor should allow the two pins to be available. I will check with my oscilloscope before I use them. 
Title: Re: Pin A6 and A7
Post by: Gates on Mar 08, 2013, 03:41 pm
A6 and A7 are floating pins. using open floating pins just needs a resistor value to them. and setup a library to set pin A6, A7 as input. If the floating pins are used it should be stated in doc or other documents related to their value as floating pin assignments.
Title: Re: Pin A6 and A7
Post by: JChristensen on Mar 08, 2013, 11:50 pm

A6 and A7 are floating pins. using open floating pins just needs a resistor value to them. and setup a library to set pin A6, A7 as input. If the floating pins are used it should be stated in doc or other documents related to their value as floating pin assignments.


Huh?
Title: Re: Pin A6 and A7
Post by: westfw on Mar 09, 2013, 02:17 am
You can't set A6/A7 as inputs, because they're ONLY connected to the A-D convert mux.  (so you can instruct the A-D converter to "read pin A6".)   No resistor required, though...
Title: Re: Pin A6 and A7
Post by: cmiyc on Mar 09, 2013, 04:38 am
A6 and A7 are 100% analog only pins and they are only available onboards with the surface mount version of the ATmega328.

Don't try to treat them as digital inputs.
Title: Re: Pin A6 and A7
Post by: Gates on Mar 09, 2013, 01:29 pm
Quote
A6 and A7 are 100% analog only pins and they are only available onboards with the surface mount version of the ATmega328.

Don't try to treat them as digital inputs.
Finally we get somewhere. I know they are analog pins. I am going to treat them kindly. I did however ask if they are reserved for other function or devices. I have seen pins like this left to float for debugging hardware/software issues. My concern is are they free to use, or involved in other devices not spoken about in the past.
Title: Re: Pin A6 and A7
Post by: JChristensen on Mar 09, 2013, 03:24 pm

Finally we get somewhere. I know they are analog pins. I am going to treat them kindly. I did however ask if they are reserved for other function or devices. I have seen pins like this left to float for debugging hardware/software issues. My concern is are they free to use, or involved in other devices not spoken about in the past.


ADC6 and ADC7 are not reserved for any other purpose, they are exactly like the other analog pins, except that they are only analog inputs (cannot also be used as digital pins) and they are only available with the 32-pin packages.