Information

• Recently plugged into a USB port.
• Drawing not more than 2.5 mA total system current from the USB bus.
Examples of allowable precursors to this set of initial conditions include:
• A powered-down device is subsequently powered-up upon being plugged into the
USB bus.
• A device in a low power mode subsequently enters run mode upon being plugged
into the USB bus.
41.5.1.2 VBUS contact detection
Once the device is plugged into a USB port, the VBUS_detect system interrupt is
triggered. System software must do the following to initialize the module and start the
charger detection sequence:
1. Restore power if the module is powered-off.
2. Set CONTROL[SR] to initiate a software reset.
3. Configure the USBDCD module by programming the CLOCK register and the
timing parameters as needed.
4. Set CONTROL[IE] to enable interrupts, or clear the bit if software polling method is
used .
5. Set CONTROL[START] to start the charger detection sequence.
41.5.1.3 Data pin contact detection
The module must ensure that the data pins have made contact because the detection
sequence depends upon the state of the USB D+ signal. USB plugs and receptables are
designed such that when the plug is inserted into the receptable, the power pins make
contact before the data pins make contact. See the following figure.
VBUS
D+
GND
VBUS
D
D+
GND
ReceptaclePlug
VBUS
D
Figure 41-10. Relative pin positions in USB plugs and receptacles
Chapter 41 USB Device Charger Detection Module (USBDCD)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 941