User's Manual

9.2.7 Detach and Wake-Up Signaling

WT12 can provide out-of-band signaling to a host controller by using the control lines

called ‘USB_DETACH’ and ‘USB_WAKE_UP’. These are outside the USB specification (no

wires exist for them inside the USB cable), but can be useful when embedding WT12 into a

circuit where no external USB is visible to the user. Both control lines are shared with PIO

pins and can be assigned to any PIO pin by setting the PS Keys PSKEY_USB_PIO_DETACH

and PSKEY_USB_PIO_WAKEUP to the selected PIO number.

USB_DETACH is an input which, when asserted high, causes WT12 to put USB_DN and

USB_DP in high impedance state and turned off the pull-up resistor on D+. This detaches

the device from the bus and is logically equivalent to unplugging the device. When

USB_DETACH is taken low, WT12 will connect back to USB and await enumeration by the

USB host.

USB_WAKE_UP is an active high output (used only when USB_DETACH is active) to wake

up the host and allow USB communication to recommence. It replaces the function of the

software USB WAKE_UP message (which runs over the USB cable), and cannot be sent

while WT12 is effectively disconnected from the bus.

USB_WAKE_UP

USB_DETACH

Port_Imbedance

USB_DPUSB_DN

USB_PULL_UP

10ms max

No max

Disconnected

Figure 14: USB_DETACH and USB_WAKE_UP Signal

9.2.8 USB Driver

A USB Bluetooth device driver is required to provide a software interface between WT12

and Bluetooth software running on the host computer. Suitable drivers are available from

www.bluegiga.com/techforum/

9.2.9 USB 1.1 Compliance

WT12 is qualified to the USB specification v1.1, details of which are available from

http://www.usb.org

. The specification contains valuable information on aspects such as

PCB track impedance, supply inrush current and product labeling.

Although WT12 meets the USB specification, CSR cannot guarantee that an application

circuit designed around the chip is USB compliant. The choice of application circuit,

component choice and PCB layout all affect USB signal quality and electrical

characteristics. The information in this document is intended as a guide and should be

read in association with the USB specification, with particular attention being given to

Chapter 7. Independent USB qualification must be sought before an application is deemed