CMX649E3 CML Microcircuits, CMX649E3 Datasheet - Page 35

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

ADM Codec
ENCODE VAD THRESHOLD Register ($E2)
Encode VAD
Threshold
(Bits 15 – 0)
ENCODE OFFSET LEVEL Register ($E3)
Encode Offset
Input
(Bits 15 - 0)
ENCODE DAC INPUT Register ($E7)
Encode DAC
Input
(Bits 15 – 0)
ENCODE ADM INPUT TEST Register ($E8)
Encoder ADM
Input Test
(Bits 7 – 0)
2002 CML Microsystems Plc
These bits directly program the threshold of detection for the Voice Activity Detector.
The number programmed into this register can range from $0 to $7FFF (0 to 32767).
The equation for the VAD threshold is:
These bits allow for an offset amount to be directly programmed. This offset amount
is useful in trimming out offsets that may occur in the on-chip analog circuitry. The
number format is 2’s complement and ranges from $8000 through $0000 to $7FFF
(-32768 to 32767).
The equation for the direct offset value is:
For normal Encoder operation this register should be loaded with a small positive
constant as outlined below.
When offset tracking is enabled (logic 1 in Bit 8 of register $E0), e.g. while encoding
an analog input signal in any format or transcoding PCM to ADM, this register
should be loaded with a small positive constant (e.g. in the range [2-16]) to allow
automatic DC nulling.
Offset tracking can be suspended by loading this register with 0 while leaving Bit 8 of
register $E0 true. This holds the current offset estimate constant. The offset
estimate can be read out via the ENCODE VAD OFFSET LEVEL OUTPUT Register
($E5).
This register allows direct access to the encoder DAC input. The number format is
2’s complement and ranges from $8000 through $0000 to $7FFF (-32768 to 32767).
This register allows ADM bits to be written via C-BUS for transcoding from ADM to
PCM. An interrupt can be enabled to inform a micro-controller when the register
needs reloading.
Register
Register
Value
Value
35
(DAC
(DAC
(Signal
Full
Full
(Offset
Detection
Scale
Scale
Voltage)
Reference
Reference
Threshold)
2
18
Voltage)
Voltage)
2
15
CMX649
D/649/1