Digital Voice Systems VC-20-ATC-10B Specifikace stáhnout pdf (Strana 26)

FAA20 Embedded NEXCOM Vocoder

Board Manual

This manual has been prepared for the Federal Aviation Administration.

FA100-00107 (March 2004) – Rev 1.0.0 Page 20

FAA20 has no such restriction. The SPRDY signal is internally pulled high

with a pull-up resistor.

Although the figure shows alignment of the FSX and FSR signals, this is not

a requirement. The maximum SCLK rate is 4.096 MHz.

The PCM clock rate can be changed “on-the-fly” to support switching

between normal and truncated timing modes; however, the transition

should be glitch-free.

5.2.3 NIB Interface

The FAA20 compressed nibble interface supports the exchange of

compressed voice data. The interface is based on that used within the

VC20; however, the FAA20 supports an expanded set of data and control

nibbles appended to the end of the nibble frame. The expanded interface

provides truncated timing control, error status, and an additional (virtual)

terminal port (COM3). Figure 7 provides the nibble interface frame format.

Figure 7: Nibble Interface Frame Format

Expanded Nibble Field Group

DCS CVD[23:0] XCS XFEC[3:0] CDATA[X:0]

VC20 Nibble Field Group

CLEN[1:0] FS[1:0]

Control/Status COM3 Terminal Data

DCS DVSI Defined Control/Status Nibble: Vocoder control and status bits. Bit assignments are identical to

VC20. The bit assignments are: DEC3=LOST, DEC2=INIT, DEC1=MUTE, DEC0=rsvd.

CVD Compressed Voice Data: Contains 23 nibbles (96-bits) of compressed voice data. Nibble orientation

and order are identical to VC20.

FS Flag Sequence: Set equal to 0xFA. Two nibble field that marks beginning of the Expanded Nibble

Interface. These flag nibbles must be correct for the FAA20 to interpret the remaining nibbles.

XCS Expanded Control/Status Nibble: Expanded control status nibble used to assert truncation mode and

provide error status. The bit assignments are: DEC3=ESTAT, DEC2=ECLEAR, DEC1=TSTAT,

DEC0=TRUN. The FAA20 uses bit transitions to set the truncation mode. To enable truncated timing

mode, force a zero-to-one bit transition for the TRUN bit in the DECx input data stream. To enable

normal timing mode, force a one-to-zero bit transition. The TSTAT bit (in the ENCx output data

stream) reflects the current timing mode with a 1 indicating truncation is active. A rising edge on the

ECLEAR bit (in the DECx input data stream) forces clearing of any latched errors and clears the FEC

counter.

XFEC FEC Error Count: For nibble output, represents 16-bit cumulative FEC decoder bit error counter (4

nibbles). Set input = 0000, for future compatibility.

CLEN Command Length: Length of CDATA expressed as nibbles. Since the CDATA field contains byte

information, the CLEN field is always even. The number of nibbles is twice the number of bytes to be

transmitted. The maximum CLEN value is 128 nibbles (or 64 bytes).

CDATA Command Data: Variable length field. Contains ASCII (or binary) bytes for terminal type command

and control. The first nibble is the most significant nibble (MSN) of the first terminal byte. The

second nibble is the least significant nibble (LSN) of the first terminal byte. The next two nibbles

contain the next terminal byte. Subsequent, nibbles contain the remaining terminal data.

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 108 109

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Digital Voice Systems VC-20-ATC-10B Specifikace Strana 26

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