CS4215 Datasheet, PDF (13/52 Pages) Cirrus Logic – 16-Bit Multimedia Audio Codec

CS4215
lected. SCLK and FSYNC must be synchronous
to the external clock.
As a third alternative, SCLK may be pro-
grammed to be the master clock input. In this
case, it must be 256 times Fs.
Serial Interface
The serial interface of the CS4215 transfers digi-
tal audio data and control data into and out of
the device. Multiple CS4215 devices may share
the same data lines. DSP’s supported include the
Motorola 56001 in network mode and a subset
of the ‘CHI’ bus from AT&T/Intel.
Serial Interface Signals
Figure 7 shows an example of two CS4215 de-
vices connected to a common controller. The
Serial Data Out (SDOUT) and Serial Data In
(SDIN) lines are time division multiplexed be-
tween the CS4215s.
The serial interface clock, SCLK, is used for
transmitting and receiving data. SCLK can be
generated by one of the CS4215s, or it can be
input from an external SCLK source. When gen-
erated by an external source, SCLK must be
synchronous to the master clock. Data is trans-
mitted on the rising edge of SCLK and is
received on the falling edge of SCLK. The
SCLK frequency is always equal to the bit rate.
The Frame Synchronizing signal (FSYNC) is
used to indicate the start of a frame. It may be
output from one of the CS4215s, or it may be
generated from an external controller. If FSYNC
is generated externally, it must be high for at
least 1 SCLK period, and it must fall at least
2 SCLKs before the start of a new frame (see
Figure 8). It must also be synchronous to the
master clock. The frequency of FSYNC is equal
to the system sample rate (see Figure 8). Each
CS4215 requires 64 SCLKs to transfer all the
data. The SCLK frequency can be set to 64, 128,
DS76F2
or 256 bits per frame, thereby allowing for 1, 2
or 4 CS4215s connected to the same bus.
In a typical multi-part scenario, one CS4215 (the
master) would generate FSYNC and SCLK,
while the other CS4215s (the slaves) would re-
ceive FSYNC and SCLK. The CLKOUT of the
master would be connected to the CLKIN of
each slave device as shown in Figure 7. Then,
the master device would be programmed for the
desired sample frequency (assuming one of the
crystals is selected as the clock source), the num-
ber of bits per frame, and for SCLK and FSYNC
to be outputs. The slave devices would be pro-
grammed to use CLKIN as the clock source, the
same number of bits per frame, and for SCLK
and FSYNC to be inputs. Since CLKOUT is al-
Controller
SCLK
SDIN
SDOUT
FSYNC
D/C
CS4215
SCLK
XTL1IN
SDIN
XTL1OUT
SDOUT
A
FSYNC
TSIN
XTL2IN
TSOUT
XTL2OUT
D/C
Master
PDN
RESET
CLKOUT
CS4215
SCLK
SDIN
CLKIN
SDOUT
FSYNC
B
TSIN
TSOUT
D/C _Slave
PDN
RESET
Figure 7. Multiple CS4215’s
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