CP3SP33SMSSLASHNOPB datasheet(222/407 Pages) TI1

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CP3SP33

SNOSCW5 – MAY 2013

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24.1.4 Serial Receive Data (SRD)

The SRD pin is used as an input when data is shifted into the Audio Receive Shift Register (ARSR). In

asynchronous mode, data on the SRD pin is sampled on the negative edge of the serial receive shift clock

(SRCLK). In synchronous mode, data on the SRD pin is sampled on the negative edge of the serial shift

clock (SCK). The data is shifted into ARSR with the most significant bit (MSB) first.

24.1.5 Serial Receive Clock (SRCLK)

The SRCLK pin is a bidirectional signal that provides the receive serial shift clock in asynchronous mode.

In this mode, data is sampled on the negative edge of SRCLK. The SRCLK signal may be generated

internally or it may be provided by an external clock source. In synchronous mode, the SCK pin is used as

shift clock for both the receiver and transmitter, so the SRCLK pin is available for use as a general-

purpose port pin or an auxiliary frame sync signal to access multiple slave devices (e.g. codecs) within a

network (see Network mode).

24.1.6 Serial Receive Frame Sync (SRFS)

The SRFS pin is a bidirectional signal that provides frame synchronization for the receiver in

asynchronous mode. The frame sync signal may be generated internally, or it may be provided by an

external source. In synchronous mode, the SFS signal is used as the frame sync signal for both the

transmitter and receiver, so the SRFS pin is available for use as a general-purpose port pin or an auxiliary

frame sync signal to access multiple slave devices (e.g. codecs) within a network (see Network mode).

24.2 Audio Interface Modes

There are two clocking modes: asynchronous mode and synchronous mode. These modes differ in the

source and timing of the clock signals used to transfer data. When the AAI is generating the bit shift clock

and frame sync signals internally, synchronous mode must be used.

There are two framing modes: normal mode and network mode. In normal mode, one word is transferred

per frame. In network mode, up to four words are transferred per frame. A word may be 8 or 16 bits. The

part of the frame which carries a word is called a slot. Network mode supports multiple external devices

sharing the interface, in which each device is assigned its own slot. Separate frame sync signals are

provided, so that each device is triggered to send or receive its data during its assigned slot.

24.2.1 Asynchronous Mode

In asynchronous mode, the receive and transmit paths of the audio interface operate independently, with

each path using its own bit clock and frame sync signal. The frame sync signals must be supplied

externally.

24.2.2 Synchronous Mode

In synchronous mode, the receive and transmit paths of the audio interface use the same shift clock and

frame sync signal. The bit shift clock and frame sync signal for both paths are derived from the same set

of clock prescalers.

24.2.3 Normal Mode

In normal mode, each rising edge on the frame sync signal marks the beginning of a new frame and also

the beginning of a new slot. A slot does not necessarily occupy the entire frame. (A frame can be longer

than the data word transmitted after the frame sync pulse.) Typically, a codec starts transmitting a fixed

length data word (e.g. 8-bit log PCM data) with the frame sync signal, then the codec’s transmit pin

returns to the high-impedance state for the remainder of the frame.

The Audio Receive Shift Register (ARSR) deserializes data received on the SRD pin (serial receiver data).

Only the data sampled after the frame sync signal are treated as valid. If the interface is interrupt-driven,

valid data bits are transferred from the ARSR to the receive FIFO. If the interface is configured for DMA,

the data is transferred to the receive DMA register 0 (ARDR0).

222

Advanced Audio Interface

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