CS8411 datasheet(18/38 Pages) CIRRUS

18 / 38 page

CS8411 CS8412

DS61F1

portant ones; whereas, the last 20 bytes are often

not used (except for byte 23, CRC).

FLAG1 and FLAG2 can be used to monitor this

buffer as shown in Figure 13. FLAG1 is set high

when CS byte 1, location 09H, is written and is tog-

gled when every other byte is written. FLAG2 is set

high after CS byte 23 is written and set low after CS

byte 3, location 0BH, is written. FLAG2 deter-

mines whether the channel status pointer is writing

to the first four-byte section of the channel status

buffer or the second four-byte section, while

FLAG1 indicates which two bytes of the section

are free to update.

The auxiliary data buffer, locations 10H to 1FH, is

written to in a cyclic manner similar to the other

buffers. Four auxiliary data bits are received per

audio sample (sub-frame) and, since the auxiliary

data is four times larger than the user data, the aux-

iliary data buffer on the CS8411 is four times larger

allowing FLAG0 to be used to monitor both.

Buffer Mode 2

In buffer mode 2, two 8-byte buffers are available

to independently buffer each channel of channel

status data. Both buffers are identical to the channel

status buffer in mode 1 and are written to simulta-

neously, with locations 08H to 0FH containing CS

data for channel A and locations 10H to 17H con-

taining CS data for channel B. Both CS buffers can

be monitored using FLAG1 and FLAG2 as de-

scribed in the BUFFER MODE 1 section.

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 6.

FLAG0

FLAG1

FLAG2

(384 Audio Samples)

Block

Left C.S. Ad.

10 11 12 13 14 15 16 17 18 19 20 21 22 23 0

C.S. Byte

(Addresses are in Hex)

(Expanded)

FLAG0

Left C.S. Ad.

User Address

0B 0C

0F 08

0F 0C

13 14

17 10

17 14

Right C.S. Ad.

FLAG1

Figure 14. CS8411 Buffer Memory Write Sequence - MODE 2

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