CS8414 datasheet(19/38 Pages) ETC

19 / 38 page

CS8413 CS8414

DS240F1

The two most significant bits in SR1 change defini-

tion for buffer mode 2. These two bits, when set, in-

dicate CRC errors for their respective channels. A

CRC error occurs when the internal calculated

CRC for channel status bytes 0 through 22 does not

match channel status byte 23. CCHG, bit 5 in SR1,

is set when any bit in the first four channel status

bytes of either channel changes from one block to

the next. Since channel status doesn’t change very

often, this bit may be monitored rather than check-

ing all the bits in the first four bytes. These bits are

illustrated in Figure 6.

Buffer Updates and Interrupt Timing

As mentioned previously in the buffer mode sec-

tions, conflicts between externally reading the

buffer RAM and the CS8413 internally writing to it

may be averted by using the flag levels to avoid the

section currently being addressed by the part. How-

ever, if the interrupt line, along with the flags, is

utilized, the actual byte that was just updated can be

determined. In this way, the entire buffer can be

read

without

concern

for

internal

updates.

Figure 15 shows the detailed timing for the inter-

rupt line, flags, and the RAM write line. SCK is 64

times the incoming sample frequency, and is the

same SCK output in master mode. The FSYNC

shown is valid for all master modes except the I2S

compatible mode. The interrupt pulse is shown to

be 4 SCK periods wide and goes low 5 SCK peri-

ods after the RAM is written. Using the above in-

formation, the entire data buffer may be read

starting with the next byte to be updated by the in-

ternal pointer.

ERF Pin Timing

ERF signals that an error occurred while receiving

the audio sample that is currently being read from

the serial port. ERF changes with the active edge of

FSYNC and is high during the erroneous sample.

ERF is affected by the error conditions reported in

SR2: LOCK, CODE, PARITY, and V. Any of

these conditions may be masked off using the cor-

responding bits in IER2. The ERF pin will go high

for each error that occurs. The ERF bit in SR1 is

different from the ERF pin in that it only causes an

interrupt the first time an error occurs until SR1 is

read. More information on the ERF pin and bit is

FSYNC

(FLAG0,1)

(FLAG2)

SCK

Left 191

Right 191

Left 0

INT

IWRITE

INT

FSF1,0

MSTR

SCED

= 1

= 1 0

Figure 15. RAM/Buffer - Write and Interrupt Timing

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