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MT8841AS Datasheet(PDF) 3 Page - Mitel Networks Corporation |
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MT8841AS Datasheet(HTML) 3 Page - Mitel Networks Corporation |
3 / 10 page MT8841 5-13 Functional Description The MT8841 Calling Number Identification Circuit (CNIC) is a device compatible with the Bellcore proposal (TR-NWT-000030) on generic requirements for transmitting asynchronous voiceband data to Customer Premises Equipment (CPE) from a serving Stored Program Controlled Switching System (SPCS) or a Central Office (CO). This data transmission technique is applicable in a variety of services like Calling Number Delivery (CND), Calling Name Delivery (CNAM) or Calling Identity Delivery on Call Waiting (CIDCW) as specified in Custom Local Area Signalling Service (CLASSSM) calling information delivery features by Bellcore. With CND, CNAM and CIDCW service, the called subscriber has the capability to display or to store the information on the calling party which is sent by the CO and received by the CNIC. In the CND service, information about a calling party is embedded in the silent interval between the first and second ring. During this period, the CNIC receives and demodulates the 1200 baud FSK signal (compatible with Bell-202 specification) and outputs data into a 3-wire serial interface. In the CIDCW service, information about a second calling party is sent to the subscriber, while they are engaged in another call. During this period, the CNIC receives and demodulates the FSK signal as in the CND case. The CNIC is designed to provide the data transmission interface required for the above service Figure 3 - Differential Input Configuration C1 R1 C2 R4 R3 R2 R5 IN+ IN- GS VRef MT8841 DIFFERENTIAL INPUT AMPLIFIER C1 = C2 = 10 nF R1 = R4 = R5 = 100 k Ω R2 = 60k Ω, R3 = 37.5 kΩ R3 = (R2R5) / (R2 + R5) VOLTAGE GAIN (AVdiff) = R5/R1 INPUT IMPEDANCE (ZINdiff) = 2 R1 2 + (1/ ωC)2 Figure 4 - Single-Ended Input Configuration at the called subscriber location either in the on-hook case as in CND, or the off-hook case, as in CIDCW. The functional block diagram of the CNIC is shown in Figure 1. Note however, for CIDCW applications, a separate CAS (CPE Alerting Signal) detector is required. In Europe, Caller ID and CIDCW services are being proposed. These schemes may be different from their North American counterparts. In most cases, 1200 baud CCITT V.23 FSK is used instead of Bell 202. Because the CNIC can also demodulate 1200 baud CCITT V.23 with the same performance, it is suitable for these applications. Although the main application of the CNIC is to support CND and CIDCW service, it may also be used in any application where 1200 baud Bell 202 and/or CCITT V.23 FSK data reception is required. Input Configuration The input arrangement of the MT8841 provides an operational amplifier, as well as a bias source (VRef) which is used to bias the inputs at VDD/2. Provision is made for connection of a feedback resistor to the op- amp output (GS) for adjustment of gain. In a single- ended configuration, the input pins are connected as shown in Figure 4. Figure 3 shows the necessary connections for a differential input configuration. User Interface The CNIC provides a powerful 3-pin interface which can reduce the external hardware and software requirements. The CNIC receives the FSK signal, demodulates it, and outputs the extracted data to the DATA pin. For each received stop bit start bit sequence, the CNIC outputs a fixed frequency clock string of 8 pulses at the DCLK pin. Each clock rising C RIN IN+ IN- GS VRef MT8841 VOLTAGE GAIN (AV) = RF / RIN RF |
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