CS8405 datasheet(35/36 Pages) CIRRUS

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CS8405A

DS469PP4

15.1.2

Serial Copy Management System

(SCMS)

In software mode, the CS8405A allows read/modi-

fy/write access to all the channel status bits. For

consumer mode SCMS compliance, the host mi-

crocontroller needs to manipulate the Category

Code, Copy bit and L bit appropriately.

In hardware mode, the SCMS protocol can be fol-

lowed by either using the COPY and ORIG input

pins, or by using the C bit serial input pin. These

options are documented in the hardware mode sec-

tion of this data sheet.

15.1.3 Channel Status Data E Buffer Access

The E buffer is organized as 24 x 16-bit words. For

each word the MS Byte is the A channel data, and

the LS Byte is the B channel data (see Figure 14).

There are two methods of accessing this memory,

known as one byte mode and two byte mode. The de-

sired mode is selected through a control register bit.

15.1.3.1

One Byte mode

In many applications, the channel status blocks for

the A and B channels will be identical. In this situ-

ation, if the user reads a byte from one of the chan-

nel's blocks, the corresponding byte for the other

channel will be the same. Similarly, if the user

wrote a byte to one channel's block, it would be

necessary to write the same byte to the other block.

One byte mode takes advantage of the often identi-

cal nature of A and B channel status data.

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 CS8405A 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 auto increment addressing

is used in combination with this mode, multi-byte

accesses such as full-block reads or writes can be

done especially efficiently.

15.1.3.2

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 CS8405A 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

input to the CS8405A's control port. The A channel

status data is first, B channel status data second.

15.2

AES3 User (U) Bit Management

The CS8405A U bit manager has two operating

modes:

Mode 1. Transmit all zeros.

Mode 2. Block mode.

15.2.1

Mode 1: Transmit All Zeros

Mode 1 causes only zeros to be transmitted in the

output U data, regardless of E buffer contents. This

mode is intended for the user who wants the output

U channel to contain no data.

15.2.2

Mode 2: Block Mode

Mode 2 is very similar to the scheme used to control

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

2 block-sized RAMs to perform the buffering. The

user has access to the first buffer, denoted the E buff-

er, through the control port. It is 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 con-

cept of A and B blocks for user data. The arrangement

thedatais

followings:

Bit15[A7]Bit14[B7]Bit13[A6]Bit12[B6]...Bit1[A0]

Bit0[B0]. The arrangement of the data in the each byte

is that the MSB is the first transmitted bit. The bit for

the A subframe is followed by the bit for the B sub-

frame.

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