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U3900BM Datasheet(PDF) 11 Page - TEMIC Semiconductors |
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U3900BM Datasheet(HTML) 11 Page - TEMIC Semiconductors |
11 / 34 page U3900BM Target Specification Rev. A2, 25-Aug-98 11 (34) CAS Detect Process (continued) Improved process: To prevent false detection from speech and music by the far and the near end (talk-off), and to detect the incoming CAS signal from the CO, polluted with speech or music by the near end (talk-down), a new feature is used: the early and up guard time. Interrupt to the µP CAS signal duration: 80 ±5 ms frequencies: 2130 Hz + 2750 Hz mixed with speech and music frequencies Early guard time Choice of 3 EGT values IN SCWID detector OUT SCWID detector 14610 Restart 3 Drops had no effect (FDD = 4 ms, FDC = 4) Up guard time Drops In signal Values permitted for drops after a successful early guard time Choice of 4 UGT values Figure 10. Timing diagram for early and up guard time Note: In the case above, the EGT counter restarts 3 times. After a sucessful 10.3-ms EGT, 3 drops occured but without any effect because the duration and the number is less than the maximum permitted. Interrupt to the µP CAS signal duration: 80 ±5 ms frequencies: 2130 Hz + 2750 Hz mixed with speech and music frequencies Early guard time Choice of 3 EGT values IN SCWID detector OUT SCWID detector 14611 Restart Down guard time Filter values permitted for spikes after a successful early guard time Choice of 4 DGT values Spikes in signal 5 Spikes had no effect (FDD = 4 ms) mixed with speech and music frequencies Figure 11. Timing diagram of early and down guard time Note: In the case above, the EGT counter restarts 3 times. After a sucessful 13.7-ms EGT, 5 spikes occured but without any effect because the duration is less than the maximum permitted. |
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