CMX649E3 CML Microcircuits, CMX649E3 Datasheet - Page 27

• Manufacturer Part Number: CMX649E3
• Description: ADM Codec
• Manufacturer: CML Microcircuits

ADM Codec
ADM Input
Select
(Bits 12 – 11)
Decoder Output
Select
(Bits 10 – 9)
Track Offset
(Bit 8)
Decoder VAD
Decay Time
Constant
(Bits 7 – 5)
2002 CML Microsystems Plc
If PCM filter interpolates, the decoder can digitally transcode a PCM signal to ADM.
If PCM filter decimates, the decoder can digitally transcode an ADM signal to PCM.
For the Decoder this bit should normally be set to a logic 0. When running the
decoder as a PCM to ADM transcoder this bit can be set to a logic 1 to allow the
transcoder to cancel a DC component in the PCM signal. A non zero DC component
will adversely affect the transcoder’s idle channel noise and should be removed or
cancelled. When enabling offset tracking ensure the decoder ADM input selection is
digital feedback, the PCM filter is set to interpolate, and the DECODE OFFSET
LEVEL Register ($D3) is loaded with a small positive constant.
Allows selection of the Voice Activity Detector decay time constant.
Bit 12
Bit 10
1
1
0
0
1
0
0
1
1
Bit 7
0
0
0
Bit 11
Bit 9
X
0
1
0
1
0
1
0
1
Bit 6
0
0
1
PCM words available in register $D6.
PCM filter interpolates linear PCM input from
burst mode interface (RX DATA pin).
This selection must be made in conjunction
with the CODEC MODE CONTROL Register
($70). Note that the burst interface expands
the PCM filter.
PCM filter interpolates linear PCM input from
C-BUS interface via the DECODE LINEAR
PCM INPUT Register($D9).
ADM decoder input from the RX DATA pin.
(Normal mode operation).
ADM decoder gets input from C-BUS via the
DECODE ADM INPUT Register ($D8). This
could be used to force in an idle pattern or to
play out an arbitrary stored signal.
(Alternate ADM input operation).
ADM input from digital feedback. When ADM
input comes from digital feedback it will
transcode from PCM to ADM. PCM filter
must be set to interpolate. In this mode the
analog interface can be powered down since
all signal processing is done digitally.
(PCM to ADM transcoding input operation).
ADM estimator output drives decoder output.
ADM estimator output summed with PCM
interpolation filter output drives decoder
output. The ADM and PCM signals can be
input from any combination of RX DATA pin
and C-BUS input registers.
Direct PCM test mode.
Interpolated PCM output.
Law or Alaw signals to linear PCM prior to
27
Bit 5
0
1
0
Selected Decoder Output
Selected ADM Input
128/(Bit Rate)
256/(Bit Rate)
512/(Bit Rate)
Decay Time Constant (ms),
CMX649
D/649/1