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DS1307 Connections
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DS1307 Connections

by Ken_F on Mon Oct 01, 2018 1:15 am

Hi, I am preparing to use a ds1307 rtc with my arduino uno and am wondering why I have to use A4 & A5 when the uno already has pins dedicated for SCL & SDA?

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Re: DS1307 Connections

by adafruit_support_bill on Mon Oct 01, 2018 5:38 am

They are the same. Pre R3 versions of the UNO did not have the dedicated SDA/SCL pins. Those were added because some of the newer Arduino processors did not use the same pins for i2c.

To make it easier to build compatible shields, they added the dedicated pins, so all shields can connect to SDA and SCLon the same pins. However, that does not mean that A4 and A5 are available for other uses. They are still the SDA and SCL pins for the UNO. The i2c signals are connected internally to both sets of pins.

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Re: DS1307 Connections

by Ken_F on Mon Oct 01, 2018 6:30 am

adafruit_support_bill:
so A4/A5 = SCL/SDA as far as the libs are concerned. Is there no way to get A4 & A5 back as analog inputs?

Ken_F
 
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Re: DS1307 Connections

by adafruit_support_bill on Mon Oct 01, 2018 6:39 am

so A4/A5 = SCL/SDA as far as the libs are concerned.

And as far as the hardware is concerned also. They are directly wired together on the board. If you are using them for i2c, you cannot also use them for analog input.;

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Re: DS1307 Connections

by Ken_F on Sun Oct 07, 2018 2:32 pm

Ok adafruit_support_bill, do you have a link to the schematic for the rev 3 board? I checked the one they list here but it seems to be either a rev 1 or rev 2 schematic hence the reason for my confusion.

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Re: DS1307 Connections

by adafruit_support_bill on Sun Oct 07, 2018 3:06 pm


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Re: DS1307 Connections

by Ken_F on Sun Oct 07, 2018 9:47 pm

Many thanks Bill, now that I have the schematic, I can see that AD4 & AD5 are directly connected to SDA & SCL respectively.

Ken_F
 
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Joined: Fri May 04, 2018 3:11 pm

Please be positive and constructive with your questions and comments.