Functional Description
POWER-UP
When power is first applied, power-on reset circuitry initializ-
es the COMBO and places it into a power-down state. All
non-essential circuits are deactivated and the DXand VFRO
outputs are put in high impedance states. To power-up the
device, a logical low level or clock must be applied to the
MCLKR/PDN pin
and
FSXand/or FSRpulses must be pres-
ent. Thus, 2 power-down control modes are available. The
first is to pull the MCLKR/PDN pin high; the alternative is to
hold both FSXand FSRinputs continuously lowÐthe device
will power-down approximately 1 ms after the last FSXor
FSRpulse. Power-up will occur on the first FSXor FSR
pulse. The TRI-STATE PCM data output, DX, will remain in
the high impedance state until the second FSXpulse.
SYNCHRONOUS OPERATION
For synchronous operation, the same master clock and bit
clock should be used for both the transmit and receive di-
rections. In this mode, a clock must be applied to MCLKX
and the MCLKR/PDN pin can be used as a power-down
control. A low level on MCLKR/PDN powers up the device
and a high level powers down the device. In either case,
MCLKXwill be selected as the master clock for both the
transmit and receive circuits. A bit clock must also be ap-
plied to BCLKXand the BCLKR/CLKSEL can be used to
select the proper internal divider for a master clock of 1.536
MHz, 1.544 MHz or 2.048 MHz. For 1.544 MHz operation,
the device automatically compensates for the 193rd clock
pulse each frame.
With a fixed level on the BCLKR/CLKSEL pin, BCLKXwill be
selected as the bit clock for both the transmit and receive
directions. Table 1 indicates the frequencies of operation
which can be selected, depending on the state of BCLKR/
CLKSEL. In this synchronous mode, the bit clock, BCLKX,
may be from 64 kHz to 2.048 MHz, but must be synchro-
nous with MCLKX.
Each FSXpulse begins the encoding cycle and the PCM
data from the previous encode cycle is shifted out of the
enabled DXoutput on the positive edge of BCLKX. After 8
bit clock periods, the TRI-STATE DXoutput is returned to a
high impedance state. With an FSRpulse, PCM data is
latched via the DRinput on the negative edge of BCLKX(or
BCLKRif running). FSXand FSRmust be synchronous with
MCLKX/R.
TABLE I. Selection of Master Clock Frequencies
BCLKR/CLKSEL
Master Clock
Frequency Selected
TP3057 TP3054
Clocked 2.048 MHz 1.536 MHz or
1.544 MHz
0 1.536 MHz or 2.048 MHz
1.544 MHz
1 2.048 MHz 1.536 MHz or
1.544 MHz
ASYNCHRONOUS OPERATION
For asynchronous operation, separate transmit and receive
clocks may be applied. MCLKXand MCLKRmust be
2.048 MHz for the TP3057, or 1.536 MHz, 1.544 MHz for the
TP3054, and need not be synchronous. For best transmis-
sion performance, however, MCLKRshould be synchronous
with MCLKX, which is easily achieved by applying only static
logic levels to the MCLKR/PDN pin. This will automatically
connect MCLKXto all internal MCLKRfunctions (see Pin
Description). For 1.544 MHz operation, the device automati-
cally compensates for the 193rd clock pulse each frame.
FSXstarts each encoding cycle and must be synchronous
with MCLKXand BCLKX.FS
Rstarts each decoding cycle
and must be synchronous with BCLKR. BCLKRmust be a
clock, the logic levels shown in Table 1 are not valid in
asynchronous mode. BCLKXand BCLKRmay operate from
64 kHz to 2.048 MHz.
SHORT FRAME SYNC OPERATION
The COMBO can utilize either a short frame sync pulse or a
long frame sync pulse. Upon power initialization, the device
assumes a short frame mode. In this mode, both frame sync
pulses, FSXand FSR, must be one bit clock period long,
with timing relationships specified in
Figure 2
. With FSXhigh
during a falling edge of BCLKX, the next rising edge of
BCLKXenables the DXTRI-STATE output buffer, which will
output the sign bit. The following seven rising edges clock
out the remaining seven bits, and the next falling edge dis-
ables the DXoutput. With FSRhigh during a falling edge of
BCLKR(BCLKXin synchronous mode), the next falling edge
of BCLKRlatches in the sign bit. The following seven falling
edges latch in the seven remaining bits. All four devices
may utilize the short frame sync pulse in synchronous or
asynchronous operating mode.
LONG FRAME SYNC OPERATION
To use the long frame mode, both the frame sync pulses,
FSXand FSR, must be three or more bit clock periods long,
with timing relationships specified in
Figure 3
. Based on the
transmit frame sync, FSX, the COMBO will sense whether
short or long frame sync pulses are being used. For 64 kHz
operation, the frame sync pulse must be kept low for a mini-
mum of 160 ns. The DXTRI-STATE output buffer is enabled
with the rising edge of FSXor the rising edge of BCLKX,
whichever comes later, and the first bit clocked out is the
sign bit. The following seven BCLKXrising edges clock out
the remaining seven bits. The DXoutput is disabled by the
falling BCLKXedge following the eighth rising edge, or by
FSXgoing low, whichever comes later. A rising edge on the
receive frame sync pulse, FSR, will cause the PCM data at
DRto be latched in on the next eight falling edges of BCLKR
(BCLKXin synchronous mode). All four devices may utilize
the long frame sync pulse in synchronous or asynchronous
mode.
In applications where the LSB bit is used for signalling with
FSRtwo bit clock periods long, the decoder will interpret the
lost LSB as ‘‘(/2’’ to minimize noise and distortion.
3