beaglebone-black - Flipbook - Page 90
BeagleBone Black
8.2 Pin Usage Consideration
This section covers things to watch for when hooking up to certain pins on the expansion headers.
8.2.1 Boot PIN
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.:
Fig. 8.3: Boot signals
If you plan to use any of these signals, then on power up, these pins should not be driven. If you do, it can
a昀昀ect the boot mode of the processor and could keep the processor from booting or working correctly.
If you are designing a cape that is intended to be used as a boot source, such as a NAND board, then you should
drive the pins to recon昀椀gure the boot mode, but only at reset. After the reset phase, the signals should not
be driven to allow them to be used for the other functions found on those pins. You will need to override the
resistor values in order to change the settings. The DC pull-up requirement should be based on the AM3358
Vih min voltage of 2 volts and AM3358 maximum input leakage current of 18uA. Also take into account any
other current leakage paths on these signals which could be caused by your speci昀椀c cape design.
The DC pull-down requirement should be based on the AM3358 Vil max voltage of 0.8 volts and AM3358
maximum input leakage current of 18uA plus any other current leakage paths on these signals.
8.2. Pin Usage Consideration
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