Transmit Signalling Circuits
Theory of Operation 4-11
5.2 High Speed Data and DTMF
The High Speed Data and DTMF waveforms are created by the µP U0101 using summer U0105-3.
Op-amp U0105-3 and resistors R0121-R0124 add up the three signals coming from the µP pins 58,
59 and 62. The output signal of U0105-3 is routed to the AFIC (U0103-13) through gate U0107-1.
Inside the AFIC the signal enters the conventional transmitter audio path at the splatter Þlter input.
Gate U0107-1 controlled by µP port PC7 (U0101-42) selects between data signal and FLAT TX
AUDIO signal. Microphone audio is muted during High Speed Data signalling.
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