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R.38A/R.38B/R.37/R.36/R.35 Modem TMS320C5000 DSP Code

Description: implements the ITU Recommendations R.38A(200b/s), R.38B(200b/s), R.37(100b/s), R.36(200-50b/s), and R.35(50b/s) for telegraphy modems. These offer transmission of FSK-modulated data in the telephone voiceband divided into sub-bands from 420Hz to 3120Hz (mean band frequencies), with independent operation of individual bands.
         The software implements separately one selected sub-band transmitter and one selected sub-band receiver from any of the R-series listed above. The software is operated by individual subroutine calls for transmitter and receiver initialisation, wherein the R.38A/R.38B/etc. channel is set, and for per-sample processing. The user is responsible for interfacing samples and data 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.

Interfaces: at the sample interface, the code can operate at 8.0kHz and 9.6kHz sample rates. At the data interface, operation can be in either Asynchronous or Synchronous mode.
      In Asynchronous mode, data is transferred with start & stop bits auto-inserted/-deleted. In Synchronous mode, data is transferred transparently, with the receiver performing clock recovery on bit transitions. In both cases, the data can be passed in multiple-bit blocks, and the nominal clock used is that of the R-series selected. At the control interface, the desired mode and channel is set on initialisation call. With the C code, control and diagnostics are provided by routine call arguments and returned values.


  • SNR for 10-6 Error Rate at R.38A 200b/s (4kHz BW noise): 4.0dB Flat Channel

Processor Load:

Function Sample rate MIPS# Data memory (words) Prog memory (words)#
Transmitter 8.0kHz 0.52 7 205
9.6kHz 0.63
Receiver 8.0kHz 1.50 39 351
9.6kHz 1.78

- #figures are for TMS320C54x operation with the assembler interface

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

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