AD1893_15 Datasheet, PDF (13/20 Pages) Analog Devices – Low Cost SamplePort 16-Bit Stereo Asynchronous Sample Rate Converter

OPERATING FEATURES
Serial Input/Output Ports
The AD1893 uses the frequency of the left/right input clock
(LR_ I) and the left/right output clock (LR_O) signals to deter-
mine the sample rate ratio, and therefore these signals must run
continuously and transition twice per sample period. (The LR_I
clock frequency is equivalent to F_SIN and the LR_O clock fre-
quency is equivalent to F_SOUT.) The other clocks (WCLK_I,
WCLK_O, BCLK_I, BCLK_O) are edge sensitive and may be
used in a gated or burst mode (i.e., a stream of pulses during
data transmission or reception followed by periods of inactivity).
The word clocks and the output bit clock are used only to write
data into or read data out of the serial ports; only the left/right
clocks are used in the internal DSP blocks. The input bit clock
is used to sample the input left/right clock. It is important that
the left/right clocks are “clean” with monotonic rising and falling
edge transitions and no excessive overshoot or undershoot which
could cause false triggering on the AD1893.
The AD1893’s flexible serial input and output ports consume
and produce data in twos-complement, MSB-first format. The
left channel data field always precedes the right channel data
field; the current channel being consumed or produced is indi-
cated by the state of the left/right clock (LR_I and LR_O). A left
channel field, right channel field pair is called a frame. The
input data field consists of 4 to 16 bits. The output data field
consists of 4 to 24 bits. The input signals are specified to TTL
logic levels, and the outputs swing to full CMOS logic levels.
The ports are configured by pin selections.
Serial I/O Port Modes
The AD1893 has pin-selectable bit clock polarity for the input
and output ports. In “normal” mode (BKPOL_I or BKPOL_O
LO) the data is valid on the rising edge. In the “inverted” mode
(BKPOL_I or BKPOL_O HI) the data is valid on the falling
edge. Both modes are shown in Figures 23 and 24.
The AD1893 uses two multiplexed input pins to control the mode
configuration of the input and output serial ports. MODE0_I
and MODE1_I control the input serial port, and MODE0_O
and MODE1_O control the output serial port as follows:
MODE0_I MODE1_I Serial Input Port Mode
0
0
Left-justified, no MSB delay, LR_I clock
triggered.
0
1
Left-justified, MSB delay, LR_I clock
triggered.
1
0
Right-justified, MSB delayed 16-bit clock
periods from LR_I clock transition, LR_I
clock triggered.
1
1
Word clock triggered, no MSB delay.
MODE0_O MODE1_O Serial Output Port Mode
0
0
Left-justified, no MSB delay, LR_O clock
triggered.
0
1
Left-justified, MSB delay, LR_O clock
triggered.
1
0
Right-justified, MSB delayed 16-bit clock
periods from LR_O clock transition, LR_O
clock triggered.
1
1
Word clock triggered, no MSB delay.
AD1893
The MSB delay is useful for I²S format compatibility and for
ease of interfacing to some DSP processors.
The AD1893 SamplePort serial ports operate in either the word
clock (WCLK_I, WCLK_O) triggered mode or left/right clock
(LR_I, LR_O) triggered mode. These modes can be utilized
independently for the input and output ports. In the word clock
triggered mode, as shown in Figure 23, after the left/right clock
is valid, the appearance of the MSB of data is synchronous with
the rising edge of the word clock. Note that the word clock is
rising edge sensitive, and can fall anytime after it is sampled HI
by the bit clock. In the left-justified left/right clock triggered
modes, as shown in Figure 24, the appearance of the MSB of
data is synchronous with the rising edge of the left/right clock
for the left channel and the falling edge of left/right clock for the
right channel. The MSB is delayed by one bit clock after the
left/right clock if the MSB delay mode is selected. In the right-
justified left/right clock triggered mode, as shown in Figure 25,
the MSB is delayed 16 bit clock periods from a left/right clock
edge, so that when there are 64 bit clock periods per frame, the
LSB is right-justified to a left/right clock edge. The word clock
is not required in the left/right clock triggered modes, and
should be tied either HI or LO. Figure 24 shows the bit clock in
the optional gated or burst mode; the bit clock is inactive be-
tween data fields, and can take either the HI state or the LO
state while inactive.
Note that there is no requirement for a delay between the left
channel data and the right channel data. The left/right clocks
and the word clocks can transition immediately after the LSB of
the data, so that the MSB of the subsequent channel appears
without any timing delay. The AD1893 is therefore capable of a
32-bit frame mode, in which both 16-bit channels are packed
into a 32-bit clock period. More generally, there is no particular
requirement for when the left/right clock falls (i.e., there is no
left/right clock duty cycle or pulsewidth specification), provided
that the left/right clock frequency equals the intended sample
frequency, and there are sufficient bit clock periods to clock in
or out the intended number of data bits.
On-Chip Oscillator
The AD1893 includes an on-chip oscillator so that the user
need only supply an external quartz crystal or ceramic resonator.
The crystal or the resonator should be tied to the XTAL_I and
XTAL_O pins of the AD1893. An external crystal oscillator can
be used to overdrive the AD1893 on-chip oscillator. The exter-
nal clock source should be applied to the XTAL_I pin, and the
XTAL_O pin should be left unconnected.
AD1893
AD1893
XTAL_I
XTAL_O
XTAL_I
XTAL_O
NC
20–64pF
16MHz
20–64pF
16MHz
16MHz CRYSTAL CONNECTION
16MHz OSCILLATOR CONNECTION
Figure 9. Crystal and Oscillator Connections
REV. A
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