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ST75C520 Datasheet(PDF) 10 Page - STMicroelectronics |
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ST75C520 Datasheet(HTML) 10 Page - STMicroelectronics |
10 / 45 page IV - FUNCTIONAL DESCRIPTION IV.1 - System Architecture The chip allows the design of a complete FAX data-pump without any external component. Aver- satile dual port RAM allows an easy interface with most micro-controllers. IV.2 - Operation IV.2.1 - Modes The modem implementation is fully compatible with FAX modulation recommendations. The modula- tion can be either Trellis Coded Modulation (TCM) as in V.17 14400, 12000, 9600, 7200bps rates, Quadrature Amplitude Modulation (QAM) as in V.29 9600, 7200, 4800 and V.27ter 4800 and 2400bps. Other modes of operation include tone and DTMF detection or generation, or speech mode. IV.2.2 - Transmitter Description The signal pulses are shaped in a dedicated filter further combined with a compromise transmit equalizer suited for transmission over strongly dis- torted lines. 3 different compromise equalizers are available and can be selected by software. IV.2.3 - Receiver Description The receiver section handles complex signals and uses a fractionally spaced complex equalizer. It is able to cope with distant modem timing drifts up to 10 -4 as specified in the ITU-T recommendations. It also compensate for frequency drift up to 10Hz and for phase jitter at multiple and simultaneous fre- quencies. IV.2.4 - Tone Generator Description Four tones can be simultaneously generated by the ST75C520. The tones are determined by their frequenciesand by the output amplitude level. A set of specific commands are also available for DTMF generation (using two of the four generators avail- able). IV.2.5 - Tone Detector Description Sixteen tones can be simultaneously detected by the ST75C520. Each of the tones to be detected is defined by the coefficients of a 4th order program- mable IIR. Detection thresholds are also program- mable from -45dBm up to -10dBm. DTMF detection is also available and is performed by a specific filter section (that requires no programming). IV.2.6 - DTMF Detector Description A DTMF Detector is included in the ST75C520, it allows detection of valid DTMF Digits. Avalid DTMF Digit is defined as a dual Tone with a total power higher than -35dBm, a duration higher than 40ms and a differential amplitude within 8dB (negative or positive). IV.2.7 - Voice Mode The ST75C520 voice mode allows the implemen- tation of enhanced telephone functions like an- swering machines. The incoming samples (9600Hz), received from the line are PCM A-law coded and writen into the dual port RAM. The outpoing samples are decompressed using the same A-law and output to the telephone line. The voice mode is entered using a CONF com- mand, it can be either transmit voice from the dual RAM Tx buffer to the telephone line, receive voice from the telephone line to the dual RAM buffer, or both of these functions simultaneously. The format of the signal is A-law coded without complementa- tion of the even bits. The buffer mechanism, be- tween the host micro-controler and the ST75C520, is identical to the mechanism used for parallel data exchanges except that it starts immediately after CONF command, the size of the transmit and received buffer, are and must be 8 bytes, there is no need for a XMIT command, and if an overrun or underrun condition occurs no error will be reported to the host processor. IV.2.8 - Analog Loop Back Test Mode In any transmission standard and serial data for- mat, the ST75C520 can be configured for analog loop back test. IV.2.9 - Low Power Mode Sleep state can be attained by a SLEEP command. Activating the reset signal will wake up the data- pump. When in sleep mode, the dual port RAM is unavailable and the clocks are disabled. When entering the low power mode, the ST75C520 stops its oscillator, all the peripherals of the DSP core are stopped in order to reduce the power consumption. The dual RAM is made inacessible. The ST75C520 can be awakened by a hardware reset. There is a maximum time of 20ms to restart the oscillator after waking up and an additional 5ms after the interrupt to be able to accept any com- mand coming from the host. ST75C520 10/45 |
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