 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
MT8885AP Datasheet(PDF) 4 Page - Mitel Networks Corporation |
|
||||||||||||||||||||||||||||||
MT8885AP Datasheet(HTML) 4 Page - Mitel Networks Corporation |
|
|
4 / 20 page  MT8885 Advance Information 4-54 0= LOGIC LOW, 1= LOGIC HIGH Table 1. Functional Encode/Decode Table Following the filter section is a decoder employing digital counting techniques to determine the frequencies of the incoming tones and to verify that they correspond to standard DTMF frequencies. A complex averaging algorithm protects against tone simulation by extraneous signals such as voice while providing tolerance to small frequency deviations and variations. This averaging algorithm has been developed to ensure an optimum combination of immunity to talk-off and tolerance to the presence of interfering frequencies (third tones) and noise. When the detector recognizes the presence of two valid tones (this is referred to as the “signal condition” in some industry specifications) the “Early Steering” (ESt) output will go to an active state. Any subsequent loss of signal condition will cause ESt to assume an inactive state. Steering Circuit Before registration of a decoded tone pair, the receiver checks for a valid signal duration (referred to as character recognition condition). This check is performed by an external RC time constant driven by ESt. A logic high on ESt causes vc (see Figure 5) to rise as the capacitor discharges. Provided that the signal condition is maintained (ESt remains high) for the validation period (tGTP), vc reaches the threshold FLOW FHIGH DIGIT D3 D2 D1 D0 697 1209 1 00 01 697 1336 2 00 10 697 1477 3 00 11 770 1209 4 01 00 770 1336 5 01 01 770 1477 6 01 10 852 1209 7 01 11 852 1336 8 10 00 852 1477 9 10 01 941 1336 0 10 10 941 1209 * 10 11 941 1477 # 11 00 697 1633 A 11 01 770 1633 B 11 10 852 1633 C 11 11 941 1633 D 00 00 (VTSt) of the steering logic to register the tone pair, latching its corresponding 4-bit code (see Table 1) into the Receive Data Register. At this point the GT output is activated and drives vc to VDD. GT continues to drive high as long as ESt remains high. Finally, after a short delay to allow the output latch to settle, the delayed steering output flag goes high, signalling that a received tone pair has been registered. The status of the delayed steering flag can be monitored by checking the appropriate bit in the status register. If Interrupt mode has been selected, the IRQ/CP pin will pull low when the delayed steering flag is active. The contents of the output latch are updated on an active delayed steering transition. This data is presented to the four bit bidirectional data bus when the Receive Data Register is read. The steering circuit works in reverse to validate the interdigit pause between signals. Thus, as well as rejecting signals too short to be considered valid, the receiver will tolerate signal interruptions (drop out) too short to be considered a valid pause. This facility, together with the capability of selecting the steering time constants externally, allows the designer to tailor performance to meet a wide variety of system requirements. Figure 5 - Basic Steering Circuit Guard Time Adjustment The simple steering circuit shown in Figure 5 is adequate for most applications. Component values are chosen according to the following inequalities (see Figure 7): tREC ≥ tDPmax + tGTPmax - tDAmin tREC ≤ tDPmin + tGTPmin - tDAmax tID ≥ tDAmax + tGTAmax - tDPmin tDO ≤ tDAmin + tGTAmin - tDPmax The value of tDP is a device parameter (see AC Electrical Characteristics) and tREC is the minimum VDD VDD St/GT ESt C1 Vc R1 tGTA = (R1C1) In (VDD / VTSt) tGTP = (R1C1) In [VDD / (VDD-VTSt)] MT8885 |
Similar Part No. - MT8885AP |
|
Similar Description - MT8885AP |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
