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 14
The Speech Compression Specialists
D
IGITAL
V
OICE
S
YSTEMS,
I
NC.
RESX RESX is the reset status output signal. It is active when the VC-20-MR2 is being
reset. The VC-20-MR2 is reset under three conditions: during power-up, as a result
of DINRS being asserted, or as a result of a Watch-Dog Timer reset. This signal is
an active low output. RESX is the VC-20-MR2's actual hard-reset signal; whereas,
RESET is a software flag that is synchronous with TXCK.
RUN
RUN is a status signal that signifies that the VC-20-MR2 is encoding and decoding
speech. This signal drives the green LED. Each data frame is divided into an
encoder window and a decoder window. The RUN signal is active within each
respective window when the VC-20-MR2 is encoding or decoding speech (see
Figure 6). RUN is synchronous with TXCK.
RXCK This is the decoder symbol clock which controls the transfer of the channel data
into the decoder. This signal must be 4.8/2.4 kHz +/- .05%. RXD, RXD1, RXD0,
FMDE, LOST, and DESLNCE must be synchronous with the rising edge of this
clock signal to within 500 ns and held stable for 100 ns after the falling edge of this
clock signal.
RXD, RXD1,
RXD0
RXD, RXD1, and RXD0 are the data signals input to the decoder. These signals
provide three bits of soft-decision information, with RXD being the MSB and
RXD0 being the LSB. These signals are each clocked into the VC-20-MR2 on each
falling edge of RXCK resulting in a total data rate of 4.8/2.4 kbps. Note that when
interfacing to a modem or other device that only provides a single bit of received
data (i.e. hard-decision) then this signal should only be connected to RXD and the
HD_SD pin should be held high.
TXCK This is the encoder data clock which controls the transfer of the channel data out of
the encoder. This signal must be 4.8/2.4 kHz +/- .05%. TXD, FMEN, FMEN,
RESET, STATUS, and RUN must be synchronous with the rising edge of this clock
signal to within 500 ns and held stable for 100 ns after the falling edge of this clock
signal.
TXD TXD is the voice data signal from the VC-20-MR2 encoder. This signals changes
state on each rising edge of TXCK, giving a total data rate of 4.8/2.4 kbps.
VAD
The VAD signal must be held low to enable the onboard Voice/Silence detection
and comfort noise generation. 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).
VFRO
VFRO is the analog speech output produced by passing the decoder output through
a 16 bit linear codec. VFRO has an analog bandwidth of 100 Hz. - 3700 Hz., and it
is constrained to be /- 1.5 volts.