RALCWI Vocoder
CMX608/CMX618/CMX638
Bit 5
HDD
If this bit is set to '1', the decoder will expect an FEC packet of hard bits. This is
a 27- or 36-byte packet, where each bit represents a decoded bit.
If this bit is cleared to '0', the decoder will expect an FEC packet of soft bits. This
is a 108- or 144-byte packet, where each decoded bit is represented by a 4-bit
LLR (Log Likelihood Ratio) value from a demodulator. See also section 6.2.
The encoder always produces hard bits, so an FEC encoded packet of 60ms will
always be 27 bytes and an FEC encoded packet of 80ms will always be 36 bytes.
This bit will be ignored if FEC is not enabled.
Bit 6
DTX
This bit controls the DTX (Discontinuous Transmission) feature. When this bit is
set to '1', DTX is enabled and the encoder can produce 2 types of frame: Data
and SID (Silence Insertion Description). When this bit is cleared to '0', the DTX
function is disabled. The same amount of data must be read from, or supplied to,
the device whether DTX is enabled or disabled. See also section 6.3. DTX is
only available when FEC is not being used and raw Vocoder frames are being
transferred. This bit will be ignored if FEC is enabled.
Bit 7
DTMFF
This bit controls the format of the 4-bit DTMF code when transferring DTMF data
into, or out of, the device. When not transferring DTMF data, the setting of this bit
is irrelevant.
Format 1 is used when this bit is cleared to '0' and Format 2 is used when this bit
is set to '1'. With Format 1, DTMF data will conform to the coding used in other
popular products, such as CML's CMX605 and Zarlink's MT8870D. With Format
2, DTMF data will be in a row:column format that corresponds to a standard
telephone keypad matrix. See section 5.7 for further information.
SDTMF register address $08
7
6
5
4
3
2
1
0
FRAME COUNT
DTMF CODE
This write-only register controls the sending of DTMF data through the Vocoder.
As an alternative to decoding DTMF tones in the input audio stream, DTMF data may be sent
directly by providing the code to be sent, and the duration, in terms of 20ms frames.
This function overrides DTMF detection, single tone recognition and vocoding. The collected
audio samples will be ignored.
After each 20ms frame is sent, the frame count value will be decremented. Special DTMF frames
will be produced until the frame count value reaches zero. See also the EFRAMEDATA ($38)
register.
If the frame count value was 15 ($F), then it is not decremented and the device will produce the
special DTMF frame until this register is written to again, either with zero in the frame count
causing it to stop, or another value other than 15, causing it to count down and then stop.
Bits 0 to 3
These bits define the DTMF tone that is to be sent.
DTMF CODE See Table 2 or Table 4.
2012 CML Microsystems Plc
37
D/608_18_38/10
CMLMICRO [ CML MICROCIRCUITS ]
