Specifications

62 SAM0025A-062397 ESS Technology, Inc.
ES1879 DATA SHEET
REGISTERS
PRELIMINARY
REGISTERS
Types of Re
g
ister Access
There are two types of audio registers in the ES1879:

Mixer registers
These registers are accessed via I/O ports Audio_Base+4h and Audio_Base+5h. Audio_Base+4h is written with
the register address. Then the register can be read/written via Audio_Base+5h. These registers control many
functions other than the mixer.

Controller registers
These registers are used to control Extended mode DMA playback and record through the first audio channel. Con-
troller registers are accessed via an extension to the Sound Blaster common interface. This interface uses I/O ports
Audio_Base+Ah, Audio_Base+Ch, and Audio_Base+Eh to transfer read data, write data/commands, and status,
respectively.
Mixer Registers
There are two types of mixer registers. Sound Blaster Pro-compatible mixer registers, as the name suggests are fully
compatible with the Sound Blaster Pro. ESS mixer registers are specific to ESS Technology, Inc.’s ES1879
Audio
Drive
®
chips, though many registers are shared throughout the
Audio
Drive
®
family of chips.
Sound Blaster Pro-Compatible Mixer Registers
This section provides a summary of Sound Blaster Pro-compatible mixer registers in the ES1879 and some comments
on the characteristics of these registers.
a.
Sound Blaster filter control bits F2, F1, and F0 have no function in the ES1879 and are ignored.
Filter Control Bits
The Sound Blaster Pro mixer has three bits that control
input and output filters. They are labeled as F0, F1, and F2
in Table 24 and Table 25. They have no function in the
ES1879 and their values are ignored.
Mixer Stereo Control Bit
Bit 1 of register 0Eh is the Mixer Stereo Control bit. It is
normally zero. Set this bit high to enable Sound Blaster
Pro-compatible stereo DAC functions. Program the DAC
sample rate to be twice the sample rate of each channel.
For example, for 22 kHz stereo, program the “sample rate”
to be 44 kHz using command 40h.
This bit enables stereo only for DMA transfer to the DAC
in Compatibility mode. It should not be used in Extended
mode.
Clear this bit after completing the stereo DMA transfer,
because this bit is unaffected by software reset (only mixer
reset).
See also “Stereo DMA Transfers in Compatibility Mode”
on page 48.
Table 24 Sound Blaster Pro-Compatible Register Summary
RegD7D6D5D4D3D2D1D0 Remark
00h Write: reset mixer Mixer reset
04h DAC play volume left x DAC play volume right x DAC playback volume
0Ah x x x x x Mic mix volume x Mic mix volume
0Ch x x F1
a
x
F0
a
ADC Source x See note for F0, F1.
0Eh x x
F2
a
x x x Stereo x See note for F2.
22h Master volume left x Master volume right x Master volume
26h FM volume left x FM volume right x Music DAC volume
28h CD (AuxA) volume left x CD (AuxA) volume right x CD (AuxA) volume
2Eh Line volume left x Line volume right x Line volume