According to the SRM page 94:
DO NOT APPLY VOLTAGE TO ANY I/O PIN WHEN POWER IS NOT SUPPLIED TO THE BOARD.
IT WILL DAMAGE THE PROCESSOR AND VOID THE WARRANTY.
NO PINS ARE TO BE DRIVEN UNTIL AFTER THE SYS_RESET LINE GOES HIGH.
I hope to have a deeper understanding on that statement. Does that only apply to specific pins such as the boot config pins?
My application requires beaglebone to be a secondary processor and it communicates with the primary processor using I2C and SPI. The beaglebone will bootup and shutdown occasionally while the primary processor will be on all the time.
I am under the impression that the pins on the beaglebone should be on high impedance when beaglebone is powered down. With I2C pulled up by default and assuming I did attempt to drive the SPI bus when BBB is powered down, is that going to destroy the processor?
When Gerald Coley wrote that down, he must have meant just that. He wrote it in big red capitals, so he must have REALLY meant it.
ANY I/O pin is not equal to SOME I/O pins
By the way If you don’t (want to) believe the SRM, why would you trust something said in a forum on the matter? This has come up a few times. You can look it up.
If you choose to remain agnostic on the matter you can also just read the Revision A5.2 version of the SRM, where this statement is missing, so you could make a case that you are right.
Yes, it only applies to ALL of the pins on the expansion headers. All SOCs have a specific power sequencing and this is related to that. You can read more about it in the AM3358 and TPS65217C datasheets.
There are no high impedance pins on the AM3358. See previous sentence.
Is the serial debug header included in the scope of the “expansion headers”?
The reason I ask is that last week I was mucking about with my serial debug cable and I was wondering if I follow the SRM, how can I capture the debug/bootup info via putty/serial connection if the BBB isn’t connected (via usb to my computer) before the BBB is powered up?
Once again many thanks for all your efforts here. I do enjoy learning* with my BBB
- last night I burt my finger because my temperture sensor was plugged in backwards … what a great learning experinece
No, it has protection on it. It is not on the expansion headers.
Thanks for the inputs! I will check out the AM3358 datasheet for more information.