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R2 MF Receiver DSP C Code

Description: 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 Backward direction
1380/1500/1620/1740/1860/1980Hz 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 C code is suitable for any processor with an ANSI-compliant C compiler. It is designed especially for efficient operation on low-cost fixed-point DSP- and general-purpose micro-processors. All data memory is specified as 16-bit integer words. Multiplies are integer 16x16-bit with 32-bit products.
        The software is in the form of 4 callable subroutines: two are for loading default parameters and initialising per-channel memory, one is for accessing any newly detected digit, and the main one is for per-sample processing. 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 code is near load-balanced so there is no significant MIPS variation per sample. To suit application, some digit detection parameters are made user-programmable. Operation can be at 8.0kHz or 9.6kHz sample rates. A user's guide is supplied.

Specification: the conditions under which R2 digit states are registered either a new digit when in the "pause" state or else a pause(non-digit) when in the "digit" state are as follows. The symbols Pth, Rtw signify that the parameter is user-programmable. All levels are per R2 tone.

Parameter: Digit detected Digit NOT detd. Notes
Frequency offset: <= 10Hz - -
Signal level threshold*: >= Pth (Pth >= -45dBm) < Pth & >= -3dBm Per tone +6dBm is peak
Twist*: <= Rtw (Rtw<= 10dB) > Rtw -
Signal duration: >= 36ms <= 18ms -
Inter-digit pause*: >= 27ms <= 18ms -

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

Processor Load:

MIPS# Data memory (words) Prog memory (bytes)#
0.93 2(common)+20(per channel) 0.71k

- #example figures from compiling for the TI TMS320C5000(C55x) DSP processor at 8.0kHz sampling

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

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