SPRUHM8K December 2013 – May 2024 TMS320F28374D , TMS320F28375D , TMS320F28376D , TMS320F28377D , TMS320F28377D-EP , TMS320F28377D-Q1 , TMS320F28378D , TMS320F28379D , TMS320F28379D-Q1
To give more flexibility, the signals External Power Enable (EPEN) and Power Fault (PFLT) were not implemented in hardware and the user must implement these signals in software. Examples of how to implement these signals in software can be found in the USB Software Guide located in C2000Ware in the \libraries\communications\usb\ directory.
When using the device controller portion of the USB controller in a system that also provides host functionality, the power to VBUS must be disabled to allow the external host controller to supply power. Usually, the EPEN signal is used to control the external regulator and must be negated to avoid having two devices driving the VBUS power pin on the USB connector.
When the USB controller is acting as a host, the USB controller is in control of two signals that are attached to an external voltage supply that provides power to VBUS. The Host controller uses the EPEN signal to enable or disable power to the VBUS pin on the USB connector. An input pin, PFLT, provides feedback when there has been a power fault on VBUS. The PFLT signal can be configured to either automatically negate the EPEN signal to disable power, or the PFLT signal can generate an interrupt to the interrupt controller to allow software to handle the power fault condition. The polarity and actions related to both EPEN and PFLT are fully configurable in the USB controller. The controller also provides interrupts on device insertion and removal to allow the Host controller code to respond to these external events.