WM9704M

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 3.2 January 2001

22

SYNC

BIT_CLK

SDATA_IN

CODEC

READY

SLOT (1)

SLOT (2)

WM9704M SAMPLES

SYNC ASSERTION HERE

AC’97 CONTROLLER

SAMPLES FIRST SDATA_IN

BIT OF FRAME HERE

END OF PREVIOUS AUDIO FRAME

Figure 12 Start of an Audio Input Frame

A new audio input frame begins with a low to high transition of SYNC as shown in Figure 12. SYNC

is synchronous to the rising edge of BIT_CLK. On the immediately following falling edge of BIT_CLK,

AC’97 samples the assertion of SYNC. This falling edge marks the time when both sides of AC-link

are aware of the start of a new audio frame.

On the next rising of BIT_CLK, AC’97 transitions

SDATA_IN into the first bit position of slot 0 (“Codec Ready” bit). Each new bit position is presented

to AC-link on a rising edge of BIT_CLK, and subsequently sampled by the AC’97 Controller on the

following falling edge of BIT_CLK.

This sequence ensures that data transitions and subsequent

sample points for both incoming and outgoing data streams are time aligned.

SDATA_IN’s composite stream is MSB justified (MSB first) with all non-valid bit positions (for

assigned and/or unassigned time slots) stuffed with 0s by the WM9704M. SDATA_IN should be

sampled on the falling edges of BIT_CLK.

SLOT 1: STATUS ADDRESS PORT

The status port is used to monitor status for the WM9704M functions including, but not limited to,

mixer settings, and power management.

Audio input frame slot 1 echoes the control register index, for historical reference, for the data to

be returned in slot 2. (Assuming that slots 1 and 2 had been tagged “valid” by the WM9704M during

slot 0).

STATUS ADDRESS PORT BIT ASSIGNMENTS:

Bit (19)

RESERVED (stuffed with 0s)

Bit (18:12)

Control register index (echo of register index for which data is

being returned)

Bit (11:2)

Variable sample rate SLOTREQ bits.

Bit (1:0)

RESERVED (stuffed with 0s)

The first bit (MSB) generated by the WM9704M is always stuffed with a 0. The following 7 bit

positions communicate the associated control register address. The next 10 bits support the AC’97

Rev 2.1 variable sample rate signalling protocol, and the trailing 2 bit positions are stuffed with 0s by

AC’97.

SLOT 2: STATUS DATA PORT

The status data port delivers 16-bit control register read data.

Bit (19:4)

Control register read data (stuffed with 0s if tagged “invalid” by

WM9704M)

Bit (3:0)

RESERVED (stuffed with 0s)

If slot 2 is tagged “invalid” by the WM9704M, then the entire slot will be stuffed with 0s by the

WM9704M.