CS4239 Datasheet, PDF (74/98 Pages) Cirrus Logic – CrystalClear™ Portable ISA Audio System

CS4239
CrystalClear^TM Portable ISA Audio System
Bus Interface
The ISA bus interface is capable of driving a 24
mA data bus load and therefore does not require
any external data bus buffering. See the Refer-
ence Design Data Sheet for a typical connection
diagram.
Volume Control Interface
Three hardware master volume control pins are
supported: volume up, volume down, and mute.
Hardware volume control is enabled by setting
the VCEN bit in the Hardware Configuration
data, byte 7 (Misc. Config. Byte). Once VCEN
is set, the XTAL1/ACDCS/DOWN pin converts
to the volume down function. The volume con-
trol pins affect the master volume control output
after the analog output mixer. The UP and
DOWN pins, when low, increment and decre-
ment the master volume. These two pins would
use SPST momentary switches. The MUTE pin
can either be momentary or non-existent where
pressing up and down simultaneously mutes the
output volume. The circuit in Figure 17, contains
optional resistors for EMI and ESD protection;
however, the capacitors are required for switch
debounce.
UP
DOWN
MUTE
100 ^Ω
10 nF
100 Ω
10 nF
100 Ω
10 nF
Up
Down
Mute
GND
Figure 17. Volume Control Circuit
Pressing the up button, increments the volume.
Pressing the down button, decrements the vol-
ume. Holding either of these buttons in the low
state causes the volume to to continue changing.
The formats are selected using the VCF1 bit in
the Hardware Configuration data, Global Config.
byte.
In the first format, where VCF1 = 0, the mute
function is a momentary switch (similar to up
and down). When MUTE goes low the master
out volume mutes if it was un-muted and vise-
versa (the mute button alternates between mute
and un-mute). If the master volume is muted and
up or down is pressed, the volume automatically
un-mutes.
In the second format, where VCF1 = 1, the
MUTE pin is not used. This is a two-button for-
mat where pressing up and down simultaneously
mutes the master volume. If the master volume
is muted and up or down is individually pressed,
the volume automatically un-mutes.
The two formats listed above as illustrated in
Figure 18.
Up
Down
Mute
GND
VCF1 = 0
Up
Down
Mute
GND
VCF1 = 1
Figure 18. Volume Control Formats
Crystal / Clock
Two pins have been allocated to allow the inter-
facing of a crystal oscillator: XTALI and
XTALO. The crystal should be designed as fun-
damental mode, parallel resonant, with a load
capacitor of between 10 and 20 pF. The capaci-
tors connected to each of the crystal pins should
be twice the load capacitance specified to the
crystal manufacturer.
An external CMOS clock may be connected to
the crystal input XTALI in lieu of the crystal.
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DS253PP2