USB Interface | 4 |
4.1Self Powered Device
Figure
The 5 to 3.3 voltage divider is required since the device GPIO pins cannot exceed 3.3 V. This voltage divider can be implemented in a number of ways. The most robust and expensive solution is to use a MAX6348
Note: If GPIOn and GPIOx are the same pin, never put the device to sleep while the USB cable is connected to the device. During sleep, the USB controller is in reset and will not respond to the host; after sleep, the device will not respond to its
Figure 4-1. Self Powered Device
USB 5V
USB UDC+
USB UDC-
USB GND
5V to 3.3V
470K
GPIOn
GPIOx
1.5K
UDC+
0ohm
(optional)
UDC-
0ohm
(optional)
Board GND
4.1.1Operation if GPIOn and GPIOx are Different Pins
Any GPIO pins can be defined as GPIOn and GPIOx. GPIOn should be a GPIO which can bring the device out of sleep. Out of reset, configure GPIOx as an input that causes the UDC+ line to float. GPIOn is configured as an input that causes an interrupt whenever a rising or falling edge is
PXA250 and PXA210 Applications Processors Design Guide |