92hdw74c2 Integrated Device Technology, 92hdw74c2 Datasheet - Page 29

• Manufacturer Part Number: 92hdw74c2
• Description: Six Channel Hd Audio Codec
• Manufacturer: Integrated Device Technology

SIX CHANNEL HD AUDIO CODEC
92HDW74C2
SIX CHANNEL HD AUDIO CODEC
1.4.17. External Volume Control
92HDW74C2 incorporates a 2-pin volume control interface. Volume up, down, and mute functions
are easily implemented using 2 push-button switches. The CODEC provides internal pull-up resis-
tors simplifying external CODEC circuitry. Also, repeat and direct modes of operation add flexibility to
the interface. The typical usage model is for front panel master volume buttons on an entertainment
PC, or case mounted hardware volume control for mobile platforms.
1.4.17.1. Theory of Operation
The codec monitors the volume up/down inputs for a change of state from high to low, and waits for
the inputs to settle. If the inputs have not settled by the end of the de-bounce period, then the value
at the end of the period is used. A 0 (low voltage) on the Down pin will decrement the volume regis-
ter, while a 0 on the Up pin will increment the volume register. If both inputs are 0 at the same time,
then the volume register will be set to its lowest value (mute). Pressing Up, Down, or both buttons at
the same time when the volume control interface is in mute mode, will cause the part to un-mute.
The de-bounce / repeat rate is selectable from 2.5Hz to 20Hz in 2.5Hz increments using the Volume
Knob VCSR0 verb (FE0) Rate bits (bits 2:0). This value is used for both de-bounce and repeat rates.
The de-bounce period is the time that the CODEC waits for the inputs to settle, and the repeat rate is
the rate at which the CODEC will increment/decrement the volume if a volume button is pushed and
held. When a falling edge is detected on either one of the volume control pins, the codec will wait for
(1/Rate) seconds for the input to settle. If the Continuous bit is set in the Volume Knob VCSR0 verb
(bit 3), then the codec will wait for the de-bounce period to expire then repeatedly increment or dec-
rement the volume register at the rate specified in the Rate bits until the button is released.
1.4.17.2. Modes of Operation
•
In Direct mode, the Volume Knob widget directly controls the volume of all of the DACs in the part.
The volume in the Volume Knob widget acts as the master volume and limits the maximum volume
for each of the DAC amplifiers. The amp gain for each of the DACs can also be adjusted using the
DAC amplifiers. However, the actual gain for an individual DAC will be the sum of the Volume Knob
volume and the DAC amplifier volume. For example, if the DAC amplifier gain is set to 0x7F (0dB)
and the Volume Knob volume is set to 0x3F (-48dB) the resulting gain would be -48dB. If the combi-
nation of gains is less than -95.25dB (the equivalent to a value of 0x0 for the DAC or Volume Knob
volume settings) then the actual gain will be -95.25dB. For example, if the Volume Knob is set to
0x3F (-48dB) and the DAC amplifier volume is set to 0x1F (-72dB) then the DAC volume will be set
to -95.25dB.
Direct mode is enabled by setting bit 7 in the Volume Knob Cntrl verb (F0F). The volume is reflected
in the Volume Knob Cntrl bits 6:0 and the step size is 0.75dB. In direct mode, software can read or
write the volume in the Volume Knob widget.
•
In indirect mode, the Volume Knob widget does not directly control the DAC amplifier gains. An
event on the volume Up/Down pins will increment/decrement the value in the Volume Knob Cntrl
verb (F0F) volume bits (bits 6:0) just as in Direct mode. However, instead of adjusting the DAC
amplifier gain, an unsolicited response is generated (if enabled) and the control software must read
DIRECT MODE
INDIRECT MODE
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92HDW74C2
PC AUDIO
V 1.0 03/08