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CF8224C Datasheet(PDF) 9 Page - Nippon Precision Circuits Inc |
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CF8224C Datasheet(HTML) 9 Page - Nippon Precision Circuits Inc |
9 / 11 page SM8224C SEIKO NPC CORPORATION —9 FUNCTIONAL DESCRIPTION The SM8224C receiver with caller ID service conforms to the Bellcore standards. It incorporates FSK demod- ulator and dual-tone detection functions in a single chip. It has a dedicated dual-tone signal input so that the FSK signal input amplification and dual-tone signal input amplification can be set independently. This allows systems can be easily constructed that provide pre- and mid-conversation information services. FSK Demodulator Calling number identification service is sent as an FSK signal, and the SM8224C FSK demodulator processes this signal. The FSK signal conforms to the following Bellcore standard. Note: S1, S0, MODE setting should be used from above combination except Test mode. Dual Tone Detector When using mid-conversation information services, 2 mixed signals of 2130Hz and 2750Hz are sent on lines L1 and L2. The SM8224C detects the 2 signals from the background noise. It uses 2 separate high-order filters with center frequencies of 2130Hz and 2750Hz to detect the presence of the signal frequencies. In series with the filters are level detectors. When the input level exceeds the preset rating, the signal is detected. When the input level is below the rating, the signal is not detected. If both the 2130Hz and 2750Hz signals are simultaneously detected, DTDET goes HIGH and starts charging the time constant circuit comprised by an external capacitor and external resistor. When the time constant cir- cuit voltage rises above a fixed voltage level, STR signal goes LOW to indicate dual tone detection. Table 1. FSK signal Parameter Description Modulation type Continuous-phase binary frequency-shift-keying Logic “1” data (mark) 1200 ± 12 Hz Logic “0” data (space) 2200 ± 22 Hz Signal level (mark) −32 to −12 dBm Signal level (space) −36 to −12 dBm Data transfer rate 1200 ± 12 baud Table 2. Function select S1 S0 MODE Function STR LOW LOW HIGH Power-down HIGH HIGH LOW LOW Dual-tone detection from DT1/DT21 1. DT1, DT2, DTQ are active in this mode only. LOW (dual tone confirmation) LOW HIGH LOW FSK and dual-tone detection from TIP/RING LOW (dual tone confirmation) HIGH HIGH LOW FSK detection from TIP/RING HIGH LOW LOW LOW Test mode2 2. Test mode should not be used. |
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