BeagleBone Green wont boot if cape connected

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Paulo Sherring

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Nov 15, 2017, 2:48:34 PM11/15/17
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Hi, all. I have a beaglebone green connected to a custom cape. I am running the latest machinekit image.
I have it all configured and runs mostly OK. I am having an issue with end switch circuitry.
The switched are connected to P8_41 and P8_42 and are connected through the circuit in the attachment (BJT with open collector, connected through load resistor and internal pullup). If the end switch is opened, the board wont boot at all. If the end switch is closed, the board boots without any further issue.
My question is: is there any blocking mechanism that prevents CPU from booting if, for example, any input is driver high?

Thanks in advance!
Paulo Sherring.
WhatsApp Image 2017-11-15 at 16.46.28.jpeg

Graham

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Nov 15, 2017, 2:59:03 PM11/15/17
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You have apparently used two pins that conflict with the boot configuration pins on the BBB, or the eMMC.

Read the "BeagleBone Black System Reference Manual" (Version C.1), pages 62, 63, 68, 82, 106, 107.

--- Graham

==

Paulo Sherring

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Nov 16, 2017, 9:24:35 AM11/16/17
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Thanks, Graham. You are correct. I have already used these pins before, but for output purposes, so, I had no issues with that. But, since using as inputs, the switches are driving the pins and changing the SYSBOOT (aka LCDDATA) bus, which I had no idea that existed for my unfortunate surprise. I guess I'll have to redesign my boards including a tristate buffer.

Paulo Sherring.
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