VBGATE
Meaning:
V
BUS
Gate.
Location:
USBCTL.6
Set:
The CPU sets this bit to make operation of the CONNECT bit (page 5)
conditional on V
BUS
being present on the V
BUS
pin.
Clear:
The CPU clears this bit to make operation of the CONNECT bit independent of
V
BUS
being valid.
POR:
VBGATE=0
Chip Reset:
No change
Bus Reset:
No change
Pwr Down:
Read-write
Programming Notes:
The USB specification states that a full-speed USB device must never power its DPLUS pullup
resistor in the absence of V
BUS
. This is most likely to occur in a self-powered device which has
its own power supply and does not directly power the pullup resistor from the V
BUS
pin. Only
when the host activates the downstream port by turning on V
BUS
is the peripheral allowed to
power its pullup resistor to indicate that it is plugged into the bus.
The VBGATE bit enforces this requirement automatically by gating the action of the CONNECT
bit with the presence of V
BUS
, as shown by the following table:
CONNECT VBGATE VBUS_DET
PULL-UP
0 X X
Not
Connected
1 0 X
Connected
1 1 0
Not
Connected
1 1 1
Connected
If VBGATE=1 and CONNECT=1, the pullup resistor will not be connected until the V
BUS
detector indicates a valid V
BUS
voltage is present.
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