Application Information (Continued)
Register Descriptions
Reset Register (00h)
Writing any value to this register causes a register reset
which changes all of the registers back to their default values. If a read is performed on this register, the LM4548 will
return a value of 0D50h indicating that National 3D Sound is
implemented, 18bit data is supported for both the ADC’s and
DAC’s, and the volume control for True Line Level Out is
supported.
Master Volume Registers (02h, 04h, 06h)
These registers allow the output levels from LINE_OUT, LNLVL_OUT and MONO_OUT to be attenuated or muted.
There are 6-bits of volume control, plus one mute bit. It is a
5-bit volume range, where each step is nominally 1.5dB and
each output can be individually muted by either setting the
most significant bit (Mx5), and/or the mute bit (D15) to ″1.″
Mute Mx5:Mx0 Function
0 00 0000 0dB attenuation
0 01 1111 46.5dB attenuation
0 1X XXXX 46.5dB attenuation
1 XX XXXX mute
Default: 8000h
PC Beep Register (0Ah)
This register controls the level of the PC_BEEP input. The
PC_BEEP can be both attenuated and muted via register
0Ah. Step size is nominally 3dB. The signal present after the
attenuation and mute block is summed into both the left and
right channels.
Mute PV3:0 Function
0 0000 0dB attenuation
0 1111 45dB attenuation
1 XXXX mute
Default: 0000h
Mixer Input Volume Registers (Index 0Ch - 18h)
These registers set the input volume levels including mute.
Each volume control is 5 bit which provides from a range of
+12dB gain to 34.5dB attenuation in 1.5dB steps. For stereo
ports, the left and right levels can be independently set. Muting a given port is accomplished by setting the MSB to 1.
Setting the MSB to 1 for stereo ports mutes both the left and
right channel. Register 0Eh has an additional 20dB boost for
a microphone level input. This is enabled by setting bit 6 of
register 0Eh to 1.
Mute Gx4:Gx0 Function
0 00000 +12dB gain
0 01000 0dB gain
0 11111 34.5dB attenuation
1 XXXXX mute
Default: 8008h (mono regs.), 8808h (stereo regs.)
Record Select Register (1Ah)
This register independently controls the source for the right
and left channel which will be recorded by the stereo ADC.
The default value is 0000h which corresponds to Mic in.
SL2:SL0 Left Record Source
0 Mic
1 CDIn(L)
2 Video In (L)
3 Aux In (L)
4 Line In (L)
5 Stereo Mix (L)
6 Mono Mix (L)
7 Phone
SR2:SR0 Right Record Source
0 Mic
1 CDIn(R)
2 Video In (R)
3 Aux In (R)
4 Line In (R)
5 Stereo Mix (R)
6 Mono Mix (R)
7 Phone
Record (Input) Gain Register (1Ch)
This registers controls the Record (Input) Gain level for the
stereo input selected via the Record Select Control Register
(1Ah). The gain can be programmed from 0dB to +22.5dB in
1.5dB steps. The level for the left and right channel can be
individually controlled. The input can also be muted by setting the MSB to 1.
Mute Gx3:Gx0 Function
0 1111 22.5dB gain
0 0000 0dB gain
1 XXXX mute
Default: 8000h
General Purpose Register (20h)
This register controls many miscellaneous functions implemented on the LM4548. The miscellaneous functions include
POP which allows the PCM to bypass the National 3D
Sound circuitry, 3D which enables or disables the National
3D Sound circuitry, MIX which selects the MONO_OUT
source, MS which selects the microphone mux source and
LPBK which connects the output of the stereo ADC to input
of the stereo DAC. LPBK provides for a digital loopthru path
when enabled.
BIT Function
POP
PCM out path and mute,0=pre3D,1=
post 3D
3D National 3D Sound on / off1=on
MIX Mono output select0=Mix,1=Mic
MS Mic select 0 = Mic1 1 = Mic2
LPBK ADC/DAC loopback
Powerdown Control / Status Register (26h)
This read/write register is used to monitor subsystem readiness and also to program the LM4548 powerdown states.
The lower half of this register is read only with a ″1″, indicating the subsection is ready. Writing to the lower 8 bits will
have no effect.
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