STAC9752 Datasheet, PDF (46/95 Pages) Integrated Device Technology – TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH HEADPHONE DRIVE, SPDIF OUTPUT MICROPHONE & JACK SENSING

STAC9752/9753
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.
Table 16. Digital PC Beep Examples
Value
1
10
25
50
100
127
255
Reg 0Ah, bits[7:0]
0x01
0x0A
0x19
0x32
0x64
0x7F
0xFF
Frequency
12,000 Hz
1200 Hz
480 Hz
240 Hz
120 Hz
94.48 Hz
47.05 Hz
This will be programmed directly by the BIOS.
IDT™
46
STAC9752/9753
TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH HEADPHONE DRIVE, SPDIF OUTPUT MICROPHONE & JACK SENSING
REV 3.3 1206