STAC9752 datasheet(46/95 Pages) IDT

46 / 95 page

STAC9752/9753

TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH HEADPHONE DRIVE, SPDIF OUTPUT MICROPHONE & JACK SENSING

IDT™

STAC9752/9753

REV 3.3 1206

TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH HEADPHONE DRIVE, SPDIF OUTPUT MICROPHONE & JACK SENSING

7.4.

PC Beep Implementation

The STAC9752/9753 offers 2 styles of PC BEEP, Analog and Digital. The digital PC Beep is a new

feature added to the AC’97 Specification Rev 2.3. This style of PC Beep will eventually replace the

analog style, thus eliminating the need for a PC Beep pin. Until this feature is widely accepted, IDT

will provide BOTH styles of PC Beep. Both PC Beep styles use Reg 0Ah. Additional information

about Reg 0Ah can be found in Section8.1.5: page51.

7.4.1.

Analog PC Beep

PC Beep is active on power up and defaults to an un-muted state. The PC_BEEP input is routed

directly to the MONO_OUT, LINE_OUT and HP_OUT pins of the CODEC. Because the PC_BEEP

input drive is often a full scale digital signal, some resistive attenuation of the PC_BEEP input is rec-

ommended to keep the beep tone within reasonable volume levels. The user should mute this input

before using any other mixer input because the PC Beep input can contribute noise to the lineout

during normal operation. This style of PC Beep is related to the AC’97 Specification Rev 2.2. To use

the analog PC Beep, a value of 00h written to bits F[7:0] (D[12:5]) disables the Digital PC Beep gen-

eration. PV[3:0] (D[4:1]) controls the volume level from 0 to 45dB of attenuation in 3dB steps.

7.4.2.

Digital PC Beep

The Digital PC Beep uses the identical register as the analog style, Reg 0Ah. This register controls

the level and frequency for the PC Beep. The beep frequency is the result of dividing the 48 KHz

clock by 4 times the number specified in F[7:0], allowing tones from 47 Hz to 12 KHz. A value of 00h

written to bits F[7:0] disables the digital PC Beep generation and enables the analog PC Beep. The

volume control bits, PV[3:0] operate identically to the analog PC Beep mode. Applying a signal to the

PC Beep pin, pin 12, may cause the digital PC Beep signal to become distorted or inaudible. When

using the digital PC Beep feature, we recommend leaving the PC Beep input pin unconnected or

connected to analog ground through a capacitor. Connecting a capacitor from the PC Beep input pin

to ground will create a more pleasing sound by changing the digital output to a more sinusoidal like

output.

This will be programmed directly by the BIOS.

Table 16. Digital PC Beep Examples

Value

Reg 0Ah, bits[7:0]

Frequency

0x01

12,000 Hz

0x0A

1200 Hz

0x19

480 Hz

0x32

240 Hz

100

0x64

120 Hz

127

0x7F

94.48 Hz

255

0xFF

47.05 Hz

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