Gibson MM516, Руководство пользователя

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MM516
User's Manual
22
Revision 1.4 7-8-2011
Hardware Description Manual
5.2 USB Interface
This is a full speed (12Mbits/s) USB interface for communicating with other compatible digital devices. BlueCore 5-
External acts as a USB peripheral, responding to requests from a master host controller such as a PC.
The USB interface is capable of driving a USB cable directly. No external USB transceiver is required. The device
operates as a USB peripheral, responding to requests from a master host controller such as a PC. Both the OHCI
and the UHCI standards are supported. The set of USB endpoints implemented can behave as specified in the USB
section of the Bluetooth v2.1 + EDR specification or alternatively can appear as a set of endpoints appropriate to
USB audio devices such as speakers.
As USB is a master/slave oriented system (in common with other USB peripherals), BlueCore 5 chip only
supports USB Slave operation.
5.2.1 USB Data Connections
The USB data lines emerge as pins USB_DP and USB_DN. These terminals are connected to the internal USB I/
O buffers of the BlueCore 5 chip, therefore, have a low output impedance. To match the connection to the
characteristic impedance of the USB cable, resistors must be placed in series with USB_DP/USB_DN and the cable.
5.2.2 USB Pull-Up Resistor
BlueCore 5 chip features an internal USB pull-up resistor. This pulls the USB_DP pin weakly high when
BlueCore 5 chip is ready to enumerate. It signals to the PC that it is a full speed (12Mbits/s) USB device.
The USB internal pull-up is implemented as a current source, and is compliant with section 7.1.5 of the USB
specification v1.2. The internal pull-up pulls USB_DP high to at least 2.8V when loaded with a 15k 5% pull-down
resistor (in the hub/host) when VDD_PADS = 3.1V. This presents a Thevenin resistance to the host of at least 900.
Alternatively, an external 1.5k pull-up resistor can be placed between a PIO line and D+ on the USB cable. The
firmware must be alerted to which mode is used by setting PSKEY_USB_PIO_PULLUP appropriately. The default
setting uses the internal pull-up resistor.
5.2.3 USB Power Supply
The USB specification dictates that the minimum output high voltage for USB data lines is 2.8V. To safely meet the
USB specification, the voltage on the VDD_USB supply terminals must be an absolute minimum of 3.1V. CSR
recommends 3.3V for optimal USB signal quality.
5.2.4 Self-Powered Mode
In self-powered mode, the circuit is powered from its own power supply and not from the VBUS (5V) line of the
USB cable. It draws only a small leakage current (below 0.5mA) from VBUS on the USB cable. This is the easier
mode for which to design, as the design is not limited by the power that can be drawn from the USB hub or root port.
However, it requires that VBUS be connected to BlueCore 5 chip via a resistor network (R vb1 and R vb2 ), so
BlueCore 5 chip can detect when VBUS is powered up. BlueCore 5 chip will not pull USB_DP high when
VBUS is off.
Self-powered USB designs (powered from a battery or PSU) must ensure that a PIO line is allocated for USB pullup
purposes. A 1.5k 5% pull-up resistor between USB_DP and the selected PIO line should be fitted to the design.
Failure to fit this resistor may result in the design failing to be USB compliant in self-powered mode. The internal
pull-up in BlueCore is only suitable for bus-powered USB devices, e.g., dongles.