CS8427-CSZ datasheet(15/60 Pages) CIRRUS

15 / 60 page

CS8427

DS477F5

5. THREE-WIRE SERIAL AUDIO PORTS

A 3-wire serial audio input port and a 3-wire serial

audio output port is provided. Each port can be ad-

justed to suit the attached device by setting the

control registers. The following parameters are ad-

justable: master or slave, serial clock frequency,

audio data resolution, left or right justification of the

data relative to left/right clock, optional 1-bit cell

delay of the 1st data bit, the polarity of the bit clock,

and the polarity of the left/right clock. By setting the

appropriate control bits, many formats are possi-

ble.

Figure 15 shows a selection of common input for-

mats, along with the control bit settings. It should

be noted that in right justified mode, the serial au-

dio output data is “MSB extended”. This means

that in a sub-frame where the MSB of the data is

'1', all bits preceding the MSB in the sub-frame will

also be '1'. Conversely, in a sub-frame where the

MSB of the data is '0', all bits preceding the MSB in

the sub-frame will also be '0'.

The clocking of the input section of the CS8427

may be derived from the incoming ILRCK word

rate clock, using the on-chip PLL. The PLL opera-

tion is described in “AES3 Receiver” on page 16. In

the case of use with the serial audio input port, the

PLL locks onto the leading edges of the ILRCK

clock.

Figure 16 shows a selection of common output for-

mats, along with the control bit settings. A special

AES3 direct output format is included, which allows

serial output port access to the V, U, and C bits em-

bedded in the serial audio data stream. The P bit is

replaced by a Z bit that marks the subframe just pri-

or to the start of each block. This format is only

available when the serial audio output port is being

clocked by the AES3 receiver recovered clock.

In master mode, the left/right clock and the serial

bit clock are outputs, derived from the appropriate

clock domain master clock.

In slave mode, the left/right clock and the serial bit

clock are inputs. The left/right clock must be syn-

chronous to the appropriate master clock, but the

serial bit clock can function in asynchronous burst

mode if desired. By appropriate phasing of the

left/right clock and control of the serial clocks,

CS8427’s can be multiplexed to share one serial

port. The left/right clock should be continuous, but

the duty cycle does not have to be 50%, provided

that enough serial clocks are present in each

phase to clock all the data bits. When in slave

mode, the serial audio output port must not be set

to right justified data.

When using the serial audio output port in slave

mode with an OLRCK input which is asynchronous

to the port’s data source, an interrupt bit (OSLIP) is

provided to indicate when repeated or dropped

samples occur.

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