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Bell 202 Data Pump Software for Texas TMS320C54x/C55x DSPs

This software implements the data pump function of the modem Bell 202. This provides half-duplex data transmission over 2 wires or full-duplex over 4 wires, at two maximum rates, one of 1800b/s and the other of 1200b/s, over the telephone network. The software is in the form of two callable subroutines, one for initialisation and one for per-sample processing of input/output samples and data bits. The user is responsible for interfacing sample and data input & output to hardware. Data and samples can be processed in blocks by making multiple sub-routine calls. The code is re-entrant to facilitate multi-channel operation. A stripped down version is available for Caller Identification (CID) use. A comprehensive user's guide is 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 interface, operation can either be in Asynchronous or in Synchronous mode. In Asynchronous mode, data is transferred in bit-blocks on a per-character basis; start & stop bits are auto-inserted/-detected. In Synchronous mode, data is transferred on a per-bit basis, with clock recovery on bit transitions being provided in the receiver. In both cases, the nominal clock used can be 1800Hz or 1200Hz. At the control interface, one 16-bit control word is used sequence operation and to set operating parameters, and one diagnostic word conveys data transfer status.

Performance:

  • SNR for 10-6 error rate at 1200b/s: 12.0dB - Flat Channel

  • SNR for 10-4 error rate at 1800b/s: 23.5dB - Flat Channel

DSP Load: