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Shared pins (I2C vs UART)
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Shared pins (I2C vs UART)

by JirkaRCK on Sun Oct 30, 2016 4:39 am

Hello,
I'm new in Beaglebone. In fact, I haven't received Beaglebone yet but need to design the modular board as soon as possible and give it to the prototype production. So I am very sorry for my noob question :-)

I am pretty confused about shared pins on expansion headers. For example, on this http://elinux.org/images/f/fe/2_I2C_Ports.PNG image, I2C-2s SCL is on both pins 19 and 21. Similar with SDA pins and I2C no. 1 pins. Can I select that i want to use pins 19 and 20 (not 21 and 22) and can I use 21 and 22 for UART2? Or does I need reserve all four pins for I2C 2?

My another question is: Can I connect MAX485 to UART5 RX and TX on expansion board, or will it corrupt booting because of pulling boot pins?

My challenge is how to connect one RTC module (I2C) and as much as possible UART devices without conflicts and without messing boot pins... This is my problem.

Thanks for every suggestion,

Jirka RCK

JirkaRCK
 
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Re: Shared pins (I2C vs UART)

by drewfustini on Sun Oct 30, 2016 11:39 pm

For the first question about pinmux, I believe that should work but would have to try it to be sure.

For the second question about pins that affect boot up, this page states:
http://elinux.org/Beagleboard:BeagleBoneBlack
"In the System Reference Manual you will find reference to Boot Pins. These pins are connected to the expansion header.
If you load or terminate these pins to the point it affects their default setting, the board will not boot."

The SRM is located here:
https://github.com/CircuitCo/BeagleBone ... f?raw=true

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Re: Shared pins (I2C vs UART)

by drewfustini on Sun Oct 30, 2016 11:43 pm

Check page 105 of the SRM.

"8.3.1 Boot Pins
There are 16 pins that control the boot mode of the processor that are exposed on the
expansion headers. Figure 63 below shows those signals as they appear on the
BeagleBone Black.:"
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Re: Shared pins (I2C vs UART)

by JirkaRCK on Mon Oct 31, 2016 3:21 am

Thank you for Your reply. I have another one small question - is it truth that I2C 1 is reserved for external EEPROMs and I should use I2C 2 for everything else? Or am I able to connect RTC via I2C 1?

JirkaRCK
 
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Re: Shared pins (I2C vs UART)

by drewfustini on Mon Oct 31, 2016 12:17 pm

JirkaRCK wrote:Thank you for Your reply. I have another one small question - is it truth that I2C 1 is reserved for external EEPROMs and I should use I2C 2 for everything else? Or am I able to connect RTC via I2C 1?


It is used for EEPROM on the capes (daughterboards) to determine which capes are connected. You could uses it though if you know you won't be using any capes.

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