CS8427-CSZ datasheet(53/59 Pages) CIRRUS

53 / 59 page

CS8427

DS477F3

When reading data in one byte mode, a single byte

is returned, which can be from channel A or B data,

depending on a register control bit. If a write is be-

ing done, the CS8427 expects a single byte to be

input to its control port. This byte will be written to

both the A and B locations in the addressed word.

One byte mode saves the user substantial control

port access time, as it effectively accesses 2 bytes

worth of information in 1 byte's worth of access

time. If the control port's autoincrement addressing

is used in combination with this mode, multi-byte

accesses such as full-block reads or writes can be

done especially efficiently.

Two Byte mode

There are those applications in which the A and B

channel status blocks will not be the same, and the

user is interested in accessing both blocks. In

these situations, two byte mode should be used to

access the E buffer.

In this mode, a read will cause the CS8427 to out-

put two bytes from its control port. The first byte out

will represent the A channel status data, and the

2nd byte will represent the B channel status data.

Writing is similar, in that two bytes must now be in-

put to the CS8427's control port. The A channel

status data is first, B channel status data second.

18.2

AES3 User (U) Bit Management

The CS8427 U bit manager has two operating

modes: transmit all zeros and block mode.

18.2.1

Mode 1: Transmit All Zeros

Mode 1 causes only zeros to be transmitted in the

output U data, regardless of E buffer contents or

U data embedded in an input AES3 data stream.

This mode is intended for the user who does not

want to transceive U data, and simply wants the

output U channel to contain no data.

18.2.2

Mode 2: Block Mode

Mode 2 is very similar to the scheme used to con-

trol the C bits. Entire blocks of U data are buffered

from input to output, using a cascade of 3 block-

sized RAMs to perform the buffering. The user has

access to the second of these 3 buffers, denoted

the E buffer, through the control port. Block mode

is designed for use in AES3 in, AES3 out situations

in which input U data is decoded using a microcon-

troller through the control port. It is also the only

mode in which the user can merge his own U data

into the transmitted AES3 data stream.

The U buffer access only operates in two byte

mode, since there is no concept of A and B blocks

for user data. The arrangement of the data is as fol-

lows:Bit15[A7]Bit14[B7]Bit13[A6]Bit12[B6]...Bit1[A

0]Bit0[B0]. The arrangement of the data in the

each byte is that the MSB is the first received bit

and is the first transmitted bit. The first byte read is

the first byte received, and the first byte sent is the

first byte transmitted. If you read two bytes from the

E buffer, you will get the following arrangement:

A[7]B[7]A[6]B[6]....A[0]B[0].

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