beaglebone-black - Flipbook - Page 94
BeagleBone Black
8.3 Signal Usage
Based on the pin muxing capabilities of the processor, each expansion pin can be con昀椀gured for di昀昀erent
functions. When in the stacking mode, it will be up to the user to ensure that any con昀氀icts are resolved
between multiple stacked cards. When stacked, the 昀椀rst card detected will be used to set the pin muxing of
each pin. This will prevent other modes from being supported on stacked cards and may result in them being
inoperative.
In «section-7-1» of this document, the functions of the pins are de昀椀ned as well as the pin muxing options.
Refer to this section for more information on what each pin is. To simplify things, if you use the default name as
the function for each pin and use those functions, it will simplify board design and reduce con昀氀icts with other
boards.
Interoperability is up to the board suppliers and the user. This speci昀椀cation does not specify a 昀椀xed function on
any pin and any pin can be used to the full extent of the functionality of that pin as enabled by the processor.
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.
8.4 Cape Power
This section describes the power rails for the capes and their usage.
8.4.1 Main Board Power
The Table 1 describes the voltages from the main board that are available on the expansion connectors and
their ratings. All voltages are supplied by connector**P9**. The current ratings listed are per pin.
Table 8.8: Expansion Voltages
Current
Name
P9
P9
Name
Current
250mA
1000mA
250mA
VDD_3V3B
VDD_5V
SYS_5V
3
5
7
4
6
8
VDD_3V3B
VDD_5V
SYS_5V
250mA
1000mA
250mA
The VDD_3V3B rail is supplied by the LDO on the BeagleBone Black and is the primary power rail for expansion
boards. If the power requirement for the capes exceeds the current rating, then locally generated voltage rail
can be used. It is recommended that this rail be used to power any bu昀昀ers or level translators that may be
used.
VDD_5V is the main power supply from the DC input jack. This voltage is not present when the board is powered
via USB. The amount of current supplied by this rail is dependent upon the amount of current available. Based
on the board design, this rail is limited to 1A per pin from the main board.
The SYS_5V rail is the main rail for the regulators on the main board. When powered from a DC supply or USB,
this rail will be 5V. The available current from this rail depends on the current available from the USB and DC
external supplies.
8.4.2 Power
A cape can have a jack or terminals to bring in whatever voltages may be needed by that board. Care should
be taken not to let this voltage be fed back into any of the expansion header pins.
It is possible to provide 5V to the main board from an expansion board. By supplying a 5V signal into the
VDD_5V rail, the main board can be supplied. This voltage must not exceed 5V. You should not supply any
8.3. Signal Usage
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