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R2 Receiver Software for Texas TMS320C54x/C55x & C2xx/C5x DSPs

This software detects dual-tone signals to ITU Q.441 R2 signalling format. R2 transmission is done by choosing tone-pair combinations from the following two 6-tone groups:

FORWARD DIRECTION: 1380/1500/1620/1740/1860/1980Hz

BACKWARD DIRECTION: 1140/1020/ 900/ 780/ 660/ 540Hz

The composite tone signal can send one of 15 digits (6C2 = 15) in each direction according to the digit code set.

The software is in the form of 5 callable subroutines: two are for loading default parameters and initialising per-channel memory, one is for setting the detection mode (Forward or Backward tone group), one is for accessing any newly detected digit, and the main one is for per-sample processing. The code can operate at sample rates of 8.0kHz or 9.6kHz. It can easily be used in a multi-channel mode: a pointer is set to each per-channel block of memory at each sub-routine call. By making multiple sub-routine calls, the code can be operated on blocks of samples. The peak-to-mean MIPS variation is low. To suit application variations, certain digit detection parameters are made user-programmable.

Performance: the conditions under which R2 digit states - either a new digit when in the "pause" state or else a pause(non-digit) when in the "digit" state - are detected (PASS) or not-detected (FAIL) are as follows. The symbols Pth(min -45dBm), Rtw(max 10dB) signify that the parameter is programmable - all levels are per R2 tone where full-scale is assumed +6dBm:

• Frequency offset: <10Hz is PASS

• Signal thresholds: <-3dBm & >Pt is PASS ; >-3dBm or <Pt is FAIL

• Twist: <Rtw is PASS ; >Rtw is FAIL

• Signal duration: >36ms is PASS ; <18ms is FAIL

• Inter-digit pause: >27ms is PASS ; <18ms is FAIL

The receiver is designed to pass the ITU Q.455 requirements.

DSP Load:

• MIPS: 0.42 - 8.0kHz sampling ; 0.50 - 9.6kHz sampling

• Data memory: 19(general)+20(per channel) words

• Program memory: 0.32k words

Availability: NOW, with user's guide containing test results - integration support can be provided.