VT1705 datasheet(21/99 Pages) ETC

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Data Sheet

VT1705 High Definition Audio Codec

7.7.3.1 Connect and Turnaround Frames

In the Connect and Turnaround Frames, the codec signals its request for initialization on SDI and then

releases SDI (turnaround) to be driven by the controller in the subsequent address frame.

Figure 17 – Connect and Turnaround Frames

The codec signals an initialization request by synchronously driving SDI high during last bit clock cycle of

Frame Sync. SDI must be asserted for the entire BITCLK cycle and must be synchronously de-asserted

the same rising edge of BITCLK as the de-assertion of the Frame Sync. The codec are only permitted to

signal an initialization request on a null input frame, a frame in which no response stream or input

streams are being sent.

In the Turnaround Frame, the codec and controllers are required to turn SDI around upon the completion

of the Connect Frame. To do this, the codec actively drives SDI low for one BITCLK cycle immediately

following the de-assertion of SYNC at the end of the Connect Frame. The codec then puts its SDI drivers

in a high impedance state at the end of the first BITCLK cycle in the Turnaround Frame. Four BITCLK

cycles before the end of the Turnaround Frame, SYNC and SID are driven high by the controller. The SDI

remains driven high through the end of the Turnaround Frame in preparation for the subsequent address

frame.

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