34825 datasheet(19/39 Pages) FREESCALE

19 / 39 page

Yes

DP->DM

SHORT?

Yes

Set

USB_CHG bit

ID_FLOAT

=1?

VBUS

Applied?

Set DP/DM

_SHORT bit

Set

VBUS_DET bit

Yes

TEST1 pin

outputs LOW

Key Released

within 1.5s?

Yes

ID Float?

Set

DETACH bit

Key

Released?

Yes

ADC =

10001 or

01111?

TEST2 pin

outputs HIGH

Set

ADC RESULT

Yes

ADC =

Key Value?

ADC =

1000x?

ADC =

0111x?

Yes

Set

ATTACH bit

Set

ATTACH bit

Set

ID_FLOAT bit

VBUS=0V

ACTIVE = 0

Yes

ID Float?

Clear

ID_FLOAT bit

ID Float

Yes

Delay

TD time

Yes

Set

ACTIVE bit

ADC =

00000?

ID shorted

to GND?

VBUS_DET

=1?

Set

ID_GND bit

Yes

DM->DP

SHORT?

Yes

Turn on

USB switches

Turn on

UART

switches

Analog Integrated Circuit Device Data

Freescale Semiconductor

34825

FUNCTIONAL DEVICE OPERATION

ACCESSORY IDENTIFICATION

Figure 14. Detailed Accessory Identification Flow Diagram

ID DETECTION

The ID detection relies on the resistance between the ID

pin and the ground (RID) inside the accessory for the

accessory detection and recognition. The nominal ID

resistance that the 34825 supports is listed in Table 6 as well

as in Table 21. The 34825 offers a 5-bit ADC for the

resistance recognition and the corresponding ADC results vs.

the RID are also listed in Table 6. The resistors are required

to have 1% or better accuracy for the ADC to recognize

successfully.

A comparator monitors the ID pin for attachment and

detachment detection. When no accessory is attached, the ID

pin is floating. An ID_FLOAT bit in the Status register stays in

the value of 1. When a resistor less than or equal to 1.0 M

is connected between the ID line and the ground, the

ID_FLOAT bit changes to 0. When the resistor is removed,

ID_FLOAT bit returns to 1. A falling-edge of the ID_FLOAT bit

represents the attachment of the accessory and the ADC is

enabled to measure the ID resistance. The ADC Result

Table 6. A rising edge of the ID_FLOAT bit represents the

detachment of the accessory.

The ADC results are broken into two groups. The values

between ‘00001’ to ‘01101’ are assigned to 13 remote-control

keys for the two accessories that support remote controllers,

as listed in Table 21. The rest of the ADC results are

assigned to various accessories. If the ADC result is one of

the remote control key values in the identification flow, it is

possible that the remote control key is stuck when the

accessory is attached.

A special Stuck Key Identification flow is designed to

resolve such an issue. As shown in the Figure 14, if the stuck

key is recognized but is released within 1.5s, the identification

flow will return to re-detect the ID line; Otherwise, the

ATTACH bit will be set and the ADC Result register has the

key result. After the key is released, the 34825 will detect the

ID resistance value again. If the accessory is still connected,

the ATTACH bit is set again and the ADC result has the ID

resistor value of the accessory.

34825 Datasheet(PDF) 19 Page - Freescale Semiconductor, Inc

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