34825 datasheet(18/39 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34825

FUNCTIONAL DEVICE OPERATION

ACCESSORY IDENTIFICATION

Accessories are categorized into two groups. Powered

accessories are accessories that supply power to the VBUS

pin while non-powered accessories do not. When the

accessory is a powered one, the VBUS-detection mechanism

will check the connection between the D+ and the D- pins as

part of the power supply type identification (PSTI). A powered

accessory may or may not have an ID resistor. A non-

powered accessory must have an ID resistor for the

identification purpose.

Accessories that have an ID resistor are grouped into

three types, as listed in Table 21.

1. Test Accessories. Such accessories include two USB

test cables that are powered accessories, and two

UART test cables that are non-powered accessories. A

test accessory has an ID resistor and four ID resistor

values are reserved for them (see Table 21 for the ID

resistor assignment). Two logic output pins, TEST1

and TEST2, are offered to indicate the attachment of

such accessories (see Table 8). The USB or the UART

switches in the IC will be turned on automatically when

a test accessory is attached.

2. Accessories with a remote controller. Two accessories

are offered to support remote control (RC) keys. The ID

resistor values are 619 k

Ω and 1.0 MΩ respectively, as

given in Table 21. Such accessories are non-powered

accessories. The 34825 monitors the ID pin

continuously for key pressing when such an accessory

is connected. 13 ID resistors are assigned to the

remote control keys, as listed in Table 21.

3. Other accessories. The remaining ID resistor values

are reserved for users to assign to their own

accessories.

The identification flow chart is shown in Figure 14. In the

Standby mode, the 34825 monitors both the ID pin and the

VBUS pin simultaneously. If an accessory is detected, the

identification state machine will find out in parallel the ID

resistor value and the type of the power supply (if a powered

accessory is attached). When the 34825 is in the Active mode

with the ACTIVE bit = 1, the host IC can force the ACTIVE bit

to 0 via the I2C bus to initiate the identification state machine.

The details on the identification flow for the VBUS-

detection mechanism and the ID detection mechanism are

described as following.

34825 Datasheet(PDF) 18 Page - Freescale Semiconductor, Inc

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