MC34708 datasheet(97/159 Pages) FREESCALE

97 / 159 page

Analog Integrated Circuit Device Data

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Freescale Semiconductor

MC34708

Functional Block Description

7.8.4.6

Control Functions

7.8.4.6.1

Timing of the Switching Action (WAIT BIT)

If the WAIT bit is '1' when the Attach interrupt bit is set, the MC34708 waits for a WAIT time before turning on the switches. The

WAIT time is programmed by the Switching Wait bits in the Timing Set 2 register. If the WAIT bit is '0' when the Attach interrupt

is generated, then the MC34708 will not turn on the switches until the WAIT bit is set to '1' by the SPI. Both cases are shown in

Figure 25.

Figure 25. Operating Waveforms of the Wait Bit

7.8.4.6.2

Automatic Switching OR Manual Switching (Switch_open & Manual S/W Bits)

When a supported accessory is identified, the default behavior of the MC34708 automatically turns on the corresponding signal

switches. The user can also choose to turn on optional signal switches manually. Switch turn on is controlled by the Manual

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S/W bit and the Switch_Open bits in the USB Manual SW/Result and USB Control/Device mode registers respectively.

If the Switch_Open bit is '0', the audio, UART, and USB switches are off.

If Manual S/W = 1, which is its reset value, the switches to be turned on and the outputs of the JIG and BOOT pins are determined

automatically by the Device Mode register, which is the identification result. If Manual S/W = 0, the switches to be turned on are

determined by the values of the USB Manual SW/Result register. The relationship between the values of the USB Manual SW/

Result register and the switches to be turned on is found in SPI/I2C Register Map section.

The values of the Switch_Open and Manual S/W bits will not affect the identification flow and the timing of the signal switching

action of the MC34708. The difference between Manual S/W = 1 and Manual S/W = 0 is what switches are turned on. In both

cases, no switches are turned on in Standby mode. If the Manual S/W bit is changed from '1' to '0' while an accessory is attached,

the already automatically turned on switches will be turned off, and the switches selected manually will be turned on. However,

writing the Manual S/W bit back to '1' in Active mode will not change the switches and outputs status. Setting the

Switch_Open = 1, sets the switches according to the Manual S/W bit.

MC34708 数据表(PDF) 97 Page - Freescale Semiconductor, Inc