On 9/7/2015 6:26 PM, rattus wrote: > This does beg one last question - as I am using expansion connector pins to > provide chip selects for numerous peripherals, what is the default state of > the AM335X pins at powerup, until the boot configuration is loaded? I've > slogged through the TRM as best I could, but want to make sure we're not > inadvertently enabling multiple chip selects that may drive competing, say, > SDOs (peripheral) into SDI (cpu) before the boot configuration is loaded. > > Ideally, they would be defaulted as inputs or tri-stated outputs, in which > case a weak pulldown on the peripheral CSn lines should keep things quiet. > Despite my best efforts at searching the 4K+ pages of the TRM, I have not > found a clear answer as to the pre-boot load default pin configuration. I > probably missed it, but my search-fu fails me.
You want the AM335x data sheet (currently SPRS717H): http://www.ti.com/lit/gpn/am3358 Refer to section 4.2, starting on page 18. You are interested in the "BALL RESET STATE" and "BALL RESET REL. STATE" (Table 4-1, pages 20-50). These indicate the state of the various pins when reset is asserted (at power up, or when being physically reset), and the value once reset is released (this value will be held until application software* changes it). The reset release state is _usually_ (but not always) the same as the state when reset is asserted. NOTES: * "Application software" can be anything from the on-chip ROM boot-loader to U-Boot to the Linux kernel to your running user-mode program. You have to also review the BBB schematics to see if there are any pull-up/pull-down resistors or other drivers or loads connected to a GPIO pin that might affect the state prior to specific configuration of any I/O pin by software. -- Charles Steinkuehler [email protected] -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
