CS8401A datasheet(8/34 Pages) ETC

8 / 34 page

may be used to avoid contention between the

transmit pointer reading the data and the user up-

dating the buffer memory. Besides indicating the

byte location being transmitted, the flags indicate

the block of memory the part is currently ad-

dressing, thereby telling the user which block is

free to be written to. Each flag has a correspond-

ing mask bit (control register 1) which, when set,

allows a transition on the flag to generate a pulse

on the interrupt pin. Flag 0 and flag 1 cause in-

terrupts on both edges whereas flag 2 causes an

interrupt only on the rising edge. Timing and

further explanation of the flags can be found in

the buffer memory section.

The two most significant bits of control register 1,

BKST and TRNPT, are used for Transparent Mode

operation of the CS8401A. Transparent Mode is used

for those applications where it is useful to maintain

frame alignment between the received and transmitted

audio data signals. In Transparent Mode

(TRNPT = "1") the MCK, FSYNC, SCK and

SDATA inputs of the CS8401A can be connected to

their corresponding outputs of the CS8411. In Trans-

parent Mode, FSYNC synchronizes the transmitter

and the receiver. The data delay through the CS8401A

is set so that three frame delays occur from the

input of the CS8411 to the output of the

CS8401A. In Transparent Mode, 32 SCK’s are

required per subframe.

Channel status block alignment between the

CS8411 and the CS8401A is accomplished by

setting BKST high at the occurrence of the Flag

2 rising edge of the CS8411. If FSYNC is a

left/right signal, BKST is sampled once per

frame; if FSYNC is a word clock, BKST is sam-

pled once per subframe. A low to high transition

of BKST (based on two successive internal sam-

ples) resets the channel status block boundary to

the beginning.

Control register 2, shown in Figure 8, contains

various system level functions. The two most

significant bits, M1 and M0, select the frequency

at the MCK pin as shown in Table 1. As an ex-

ample, if the audio sample frequency is 44.1 kHz

and M0 and M1 are both zero, MCK would then

be 128

× the audio sample rate or 5.6448 MHz. The

next bit (5) in control register 2, V, indicates the valid-

ity of the current audio sample. According to the

Figure 4. CS8401A Block Diagram

Control

and Flags

4 X 8

Buffer

Memory

28 X 8

Parity

Preamble

Timing

Mux

MCK

TXP

TXN

Serial

Port

Audio

Logic

FSYNC

SCK

SDATA

D0-D7

A4-A0

C Bits

Control

Read

Address

Generator

Interrupt

RD/WR

INT

Aux

CRC

Biphase

Mark

Encoder

Line

Driver

21-24, 1-4

9-13

U Bits

Validity

Prescaler

IMCK

CS8401A

DS60F1

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