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Analog Integrated Circuit Device Data
Freescale Semiconductor
110
PC34708
Functional Block Requirements and Behaviors
Mini/Micro USB Interface Description and Application Information
7.10.5 Stuck Key Identification
When the ADC conversion is finished and the ADC result is found to be a value corresponding to a remote control key of Audio
Type 1 cable, a stuck key process flow will be initiated to determine whether a remote control key is stuck and to inform the
baseband of the stuck key status.
Figure 24 shows the stuck key process flow. If the stuck key is detected to be released within 1.5 s, the flow will return to re-start
the ID identification flow. Otherwise, a Stuck_Key Interrupt is set. When the key is released, a Stuck_Key_RCV Interrupt is
generated, and the identification flow is re-started to determine the ID resistance of the attached cable.
Figure 24. Stuck Key Process Flow Diagram
7.10.6 Power Supply Type Identification
The PSTI (Power Supply Type Identification) circuit is used in Active mode to identify the type of the connected power supply.
The PSTI circuit first detects whether the DP and DM pins are shorted. If the DP and DM pins are found to be shorted, the PSTI
circuit will continue to determine whether DP and DM pins are a forward short or reverse short. The detection result, together
with the ID detection result, is used to determine what powered accessory is connected.
The PSTI circuit is shown in
Figure 25. Its operation is described as follows.
When the PC34708 detects that the VBUS_DET bit is set, the PSTI identification flow starts.
1. Wait for a Detection Delay tD (programmable in the USB Time Delay register).
2. During tD, check to see whether ID_FLOAT = 0. If yes, then wait for the ID_DET_END to be set and check whether the
attached accessory is an A/V cable.
3. If the result is an A/V cable, set the A/V_CHG and ATTACH interrupt bits, as well as the A/V bit in USB Device Type/Status
register, to inform the baseband and finish the identification flow. If not, go to step 4.
4. Enable the PSTI (PSTI_EN set to '1') at t1. When PSTI_EN rises, the SW1 switch is turned on to drive the VDAT_SRC
data source voltage to DP line. In the meantime, the SW2 switch is turned on so the IDAT_SINK current source sinks a
current from the DM line. At t2, the PSTI starts to compare the DM line voltage with references VDAT_REF and VCR_REF.
If the DM line voltage stays above VDAT_REF, but below VCR_REF for 20 ms continuously before t4, which means that
the DP and DM pins are shorted, the DP/DM_short signal is set to '1' at t3. Go to step 5. If the DP and DM are not shorted,
the VBUS detection completes at t4 and the VBUS_DET_END is set to '1'. The state machine will go to step 6 to
determine the type of accessory, based on the DM voltage.