Nokia 6255 Description And Troubleshooting page 34

6255/6255i6256/6256i (RM-19)
Baseband Description and Troubleshooting
The USB consists of four signals:
Signal
Vbus
D+
D-
GND
When the mobile terminal is attached to a USB host, the host provides a 5V supply at the
Vbus pin of the system connector. The NUT indicates the presence of the host to the
W2FC by altering the state of Vp and Vm as shown in Table 11.
After the USB host is connected, D+ and D- are pulled to GND by 15kW resistors at the
host end. In turn, the Vp and Vm are pulled low. Any state other than Vp=Vm=1
generates a wake request interrupt. When the NMP software receives this interrupt, it
enables the 48MHz clock and wakes the MCU from deep sleep.
When the NMP software is ready to communicate with the USB host, it asserts the
1.3kW pull up on the D+ signal by instructing the W2FC to assert its PUENO signal. The
NUT detects this and ties the D+ signal to a 3.3V supply through the 1.3kW pull up. The
W2FC brings the NUT out of suspend by setting SUSPEND low. The NUT now draws the
majority of its current from the USB host 5V supply.
The USB host detects a high state on the D+ line and recognizes that a USB device is
attached. 100ms later, the USB host drives a reset for 10ms by driving D+ and D- low.
Following the reset, the USB host starts to drive data across the D+ and D- lines,
requesting configuration information from the device. The NUT level shifts and
conditions this data, presenting it to the W2FC on its RCV, Vp and Vm pins.
Once the W2FC has decoded the received data, it begins transmitting back to the USB
host by asserting the NUT's active low OE pin and then driving data on the NUT's VO pin.
After some level shifting and conditioning, the NUT drives the D+ and D- lines with this
data.
The USB Tx and Rx continue in this fashion controlled by the USB host.
Page 34
Table 10: USB Signals
Description
5V Power supply from host to device
Differential data signal (swings between 0 and +3.3V)
Differential data signal (swings between 0 and +3.3V)
Ties host and device ground together
Table 11: Vp and Vm States
Vcc Vp
0V Logic 1
5V Same logic as D+
©2005 Nokia Corporation
Nokia Customer Care
Vm
Logic 1
Same logic as D-
Company Confidential Issue 2 05/2005