Digital Voice Systems VC-20-MR2, Руководство пользователя

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Section 6 – Advanced Features
VC-20 AMBE™ Vocoder Board User’s Manual
page 13
The Speech Compression Specialists
D
IGITAL
V
OICE
S
YSTEMS,
I
NC.
Figure 1: Voice/Silence Detection Timing
FMDE This is the decoder frame flag which identifies the beginning of the channel input
frame. FMDE must be held high for one clock period of RXCK every 96 clock
cycles (20 ms).
FMEN This is the encoder frame flag which identifies the beginning of the channel output
frame. FMEN must be held high for one clock period of TXCK every 96 clock
cycles (20 ms).
FS The FS signal can be held low to signal the encoder that the next 20 ms frame will
be stolen, i.e. replace with inband data. This allow the encoder to compensate for
the missing frame in subsequent frames, thereby improving overall quality. This
signal is sampled on the falling edge of the first clock cycle of each 20 ms encoder
frame. If low, the encoder assumes the next frame will be stolen and outputs a
special frame steal packet on TXD. If left unconnected, this signal is pulled
internally to the disabled state (high).
GND, AGND GND is the digital ground signal and AGND is the analog ground signal. These
signals are connected on the VC-20-MR2.
HD_SD The HD_SD signal must be set low to enable soft-decision decoding or held high to
disable soft decision decoding. This signal is sampled on the falling edge of the
first clock cycle of each 20 ms decoder frame. If left unconnected, this signal is
pulled internally to its inactive state (high).
LOST The LOST flag is active if the current frame of channel data is invalid, in which
case the decoder ignores the current frame of channel data and performs a frame
repeat. This signal is sampled on the falling edge of the first clock cycle of each 20
ms decoder frame.
RATE The RATE signal controls the data rate of the voice codec. The two available rates
are 4800 bps. and 2400bps. Holding this signal HIGH runs the 4800bps. system
and holding it LOW runs the 2400bps. system. This signal is sampled on the falling
edge of the first clock cycle of each 20 ms encoder frame.
FMEN
Silence Voice Voice Voice Silence
ENSLNCE