It's best to use an interrupt-capable GPIO for this. If the USB module doesn't have a dedicated VBUS pin you can use a resistor voltage divider to reduce the 5V to something compatible with your 3.3V IO pins. The USB module should provide a way to do this. Only connect the DP pull-up to the line when VBUS is high. If you need to pass certification, you'll have to do at least the following: this is a personal project), you can probably get away with connecting the DP and DM pins directly to the jack and leaving VBUS unconnected.
The answer to this mainly depends on whether you need to pass USB certification or not. If no dedicated pin, a GPIO should be used to provide this functionality. For the ATUC256L4U I couldn't locate this pin right away, maybe more examination is required. Many Atmel's MCU do have a dedicated "VBUS_detect" input pin for USB interface. Many older devices would ignore this requirement and pull-up D+ to 3V with 1.5k resistor regardless, thus violating USB specifications. The point is that a good USB device should not source any voltage or significant current on any USB interface pins until it is connected to host and receives valid VBUS. If this signal is misused (not used for this purpose), the device will have no means to detect the connection, to assert the pull-up on D+ starting USB connect negotiation (if it has self power). But the other important function of this pin is to inform the device that it was connected to a host. One function of VBUS is to supply power to the device (if it does not have its own).
The main concern for a USB-compliant device is what to do with VBUS signal (Vcc on the diagram).
#Micro usb on ireader yksh serial#
However, depending on type of USB transceivers, a serial resistors (22-27 Ohms) with small caps (10pF) to ground might be helpful to keep the port reliable and ESD protected, maybe even without any extra suppressors. The FS mode does not require too much care about board traces as transmission lines. Therefore, as USB device, it can have either attached cable with Type-A plug, or female receptacle of B-type, either full-size B, or micro-B, since more reliable and sturdy mini-B has been obsoleted and retired by USB.org. This particular processor, ATUC256L4U, has support only as a USB device, and only at Full-Speed (12Mbps) rate.
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