USB bridge circuit gating RID
A physical layer integrated circuit (PHY), including an accessory charger adapter (ACA) bridge circuit to communicate with an ACA via a universal serial bus (USB) cable having at least an ID pin and a VBUS pin. The PHY is also to communicate with an ACA-agnostic USB controller configured to act as an A-device or as a B-device. The ACA includes a USB accessory port. The ACA bridge circuit includes detection and control logic configured to detect, based on a resistance sensed on the ID pin, that a B-device is connected to the USB accessory port of the ACA and, as a result of such a detection, generate a signal to the USB controller that causes the USB controller to act as an A-device and ignore a VBUS drive signal from the USB controller.
1. A physical layer integrated circuit (PHY), comprising:
an accessory charger adapter (ACA) bridge circuit to communicate with an ACA via a universal serial bus (USB) cable having at least an ID pin and a VBUS pin and to communicate with an ACA-agnostic USB controller configured to act as an A-device or as a B-device, the ACA including a USB accessory port, and the ACA bridge circuit including detection and control logic configured to:
detect, based on a resistance sensed on the ID pin, that a B-device is connected to the USB accessory port of the ACA and, as a result of such a detection, generate a signal to the USB controller that causes the USB controller to act as an A-device and ignore a VBUS drive signal from the USB controller that, if not ignored, would cause the PHY to drive the VBUS pin; and
detect, based on a resistance sensed on the ID pin, that an off/idle A-device or nothing is connected to the USB accessory port of the ACA and, as a result of such a detection, modify a signal to the USB controller that prevents the USB controller from being aware of a voltage on the VBUS pin;
the bridge circuit including an RID_A resistance detection circuit configured to output an asserted signal when the resistance sensed on the ID pin indicates that a B-device is connected to the USB accessory port of the ACA and a USB charger is connected to a charger port of the ACA or a deasserted signal in any other case; and
an RID_GND resistance detection circuit configured to output a deasserted signal when the ID pin is grounded or an asserted signal in any other case;
wherein the detection and control logic produces an IDGND control signal by performing a logical AND operation of the output of the RID_GND resistance detection circuit and the inverse of the output of the RID_A resistance detection circuit; and wherein the IDGND control signal being deasserted causes the USB controller to act as an A-device.
2. The PHY of claim 1 wherein the detection and control logic is further configured to, as a result of a detection that an off/idle A-device is connected to the USB accessory port of the ACA, mask signals from the USB controller that would otherwise cause a conflict on the VBUS pin.
3. The PHY of claim 2 wherein the signals from the USB controller that would otherwise cause a conflict on the VBUS pin comprise signals that enable session request protocol (SRP) communication on the VBUS pin.