CYW20704
5.3 USB Interface
5.3.1 Features
The following USB interface features are supported:
■ USB Protocol, Revision 2.0, full-speed compliant with LPM support (up to 12 Mbps)
■ Global and selective suspend and resume with remote wake-up
■ Bluetooth HCI
■ HID, DFU, UHE (proprietary method to emulate an HID device at system boot)
■ Integrated detach resistor
Note: If the USB transport is not used, tie the CYW20704 USB pins and VDD_USB to ground.
5.3.2 Operation
The CYW20704 can be configured to boot up as a single USB peripheral, and the host detects a single USB Bluetooth device.
The CYW20704 can boot up showing the independent interfaces connected to logical USB devices internal to the CYW20704—a
generic Bluetooth device, a mouse, and a keyboard. In this mode, the mouse and keyboard are emulated devices, since they con-
nect to real HID devices via a Bluetooth link. The Bluetooth link to these HID devices is hidden from the USB host. To the host, the
mouse and/or keyboard appear to be directly connected to the USB port. This Cypress proprietary architecture is called USB HID
Emulation (UHE).
The USB device, configuration, and string descriptors are fully programmable, allowing manufacturers to customize the descriptors,
including vendor and product IDs, the CYW20704 uses to identify itself on the USB port. To make custom USB descriptor informa-
tion available at boot time, stored it in external NVRAM.
In the single USB peripheral operating mode, the Bluetooth device is configured to include the following interfaces:
Interface 0
Contains a Control endpoint (Endpoint 0x00) for HCI commands, a Bulk In Endpoint (Endpoint 0x82) for receiving
ACL data, a Bulk Out Endpoint (Endpoint 0x02) for transmitting ACL data, and an Interrupt Endpoint (Endpoint
0x81) for HCI events.
Interface 1
Interface 2
Contains Isochronous In and Out endpoints (Endpoints 0x83 and 0x03) for SCO traffic. Several alternate Interface
1 settings are available for reserving the proper bandwidth of isochronous data (depending on the application).
Contains Bulk In and Bulk Out endpoints (Endpoints 0x84 and 0x04) used for proprietary testing and debugging
purposes. These endpoints can be ignored during normal operation.
5.3.3 UHE Support
The CYW20704 supports the USB device model (USB 2.0-compatible, full-speed compliant with LPM support). Optional mouse and
keyboard interfaces utilize Cypress’s proprietary USB HID Emulation (UHE) architecture, which allows these Bluetooth devices
appear as standalone HID devices even though connected through a Bluetooth link.
The presence of UHE devices requires the CYW20704 to be configured as a composite device (Composite mode). In this mode, the
Bluetooth mouse and keyboard interfaces are independently controlled and appear as standalone logical devices.
Cypress’s standard composite configuration uses the following layout:
■ Interface 0—Keyboard
■ Interface 1—Mouse
■ Interface 2/3/4—Bluetooth (as described above)
When operating in Composite mode, every interface does not have to be enabled—each can be optionally enabled. The configura-
tion record in NVRAM determines which devices are present.
Document Number: 002-14786 Rev. *E
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