Digital Voice Systems VC-20-MR2, User Manual, Page: 20 / 32

Section 6 – Advanced Features
VC-20 AMBE™ Vocoder Board User’s Manual
page 12
The Speech Compression Specialists
D
IGITAL
V
OICE
S
YSTEMS,
I
NC.
DESLNCE The DESLNCE flag signals the decoder that silence has been detected during the
current frame. If DESLNCE is held low, the decoder ignores the current frame of
channel data and outputs comfort noise on VFRO. This signal is sampled on the
falling edge of the first clock cycle of each 20 ms decoder frame. Note that if
DESLNCE is connected to ENSLNCE either directly or through a voice activated
channel, then adaptive comfort noise generation is enable whenever DESLNCE is
low.
DINRS DINRS is a VC-20-MR2 reset signal. An active high level on DINRS for a duration
of at least 300 ns will reset the VC-20-MR2. DINRS will generate RESX and
RESET. The VC-20-MR2 will pull this signal to its inactive state (low) when it is
not being driven by an external source (it may be left unconnected if not being
used).
DTMF_DAT
If the VC-20 detects a dtmf tone, it outputs four bits of data identifying the tone on
the DTMF_DAT signal (see Section 7). The data is output during the four clock
cycles when DTMF_DET is high. The data is synchronous with the rising edge of
TXCK. This signal should be ignored when DTMF_DET is inactive.
DTMF_DET
The DTMF_DET flag is activated by the encoder if it detects a dtmf tone on VRXI.
The DTMF_DET is brought high on a rising edge of TXCK and held high for four
clock cycles. During this time the DTMF data is output on DTMF_DAT. The
DTMF_DET flag is only output once for each continuous dtmf tone that is detected.
DTMF_DET can only be active during the first four clock cycles of a 20 ms data
frame.
ECHO The ECHO signal must be held low to enable the onboard 5 ms echo cancellor.
This signal is sampled on the falling edge of the first clock cycle of each 20 ms
encoder frame. If left unconnected, this signal is pulled internally to the disabled
state (high).
ENSLNCE
The ENSLNCE signal indicated whether the encoder has detected voice or silence
during the current frame. A high value (inactive) indicates voice was detected
while an active low value indicates silence (or background noise) was detected.
The ENSLNCE signal changes state at the beginning of each channel output frame
as indicated by FMEN. This signal can be connected to DESLNCE to enable
adaptive comfort noise generation. The ENSLNCE flag is deactivated by the
encoder 40 ms. prior to the onset of voice activity as shown in Figure 1.