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V.8 Modem TMS320C5000 DSP Code

Description: implements the ITU modem Recommendation V.8 for the standard 2-wire telephone network. V.8 is used by data modems / fax machines developed since the early 1990s to exchange operational menus. The V.8 signals are the initial sequence exchanged following connect-to-line. They start with a modified version of the 2100Hz auto-answer signal for disabling echo-control devices. The operational menus are then exchanged using V.21 300b/s FSK modulation. The Calling channel uses 980Hz(Mark) and 1180Hz(Space) tones whilst the Answering channel uses 1650Hz(Mark) and 1850Hz(Space) keying tones. As part of the menu exchange in V.8, the highest common denominator modulation mode is chosen.
         The assembler software is in the form of callable subroutines, eg for initialisation and for main-routine processing of input/output sample blocks and data menus. The user is responsible for interfacing samples to hardware. In the assembler interface, the code is re-entrant to facilitate multi-channel operation. A C-callable wrapper can also be provided, allowing individual channels to be called from C to process multiple sample blocks. A comprehensive user's guide together with example application files are provided with the code. Test results are available.

Interfaces: at the sample interface, the code can operate at 8.0kHz and 9.6kHz sample rates. At the data array interface, operational menus are loaded and accepted as octets in parameter groupings as per V.8. Start-stop bits are added and discarded in the V.8 code.
         At the control interface, the assembler code has one 16-bit control word to sequence operation and to set operating parameters, and one diagnostic word to convey the V.8 handshake status and to provide a modulation mode listing of the V.8 negotiation result. With the C wrapper, control and diagnostics are provided by routine call arguments and returned values.

Performance:

  • SNR for 10-6 Error Rate at 300b/s (4kHz BW noise): 5.0dB Flat Channel

Processor Load:

Sample rate MIPS# Data memory (words) Prog memory (bytes)#
8.0kHz 4.7 128 1.2k (incl. V.21 code)
9.6kHz 7.5

- #figures are for TMS320C54x operation with the assembler interface

Availability: NOW - sale is under licence - integration support offered

 
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