1-8 (No.RA003)2.1.6 Signaling Circuit2.1.6.1 Encode Low-speed data (QT, DQT)Low-speed data is output from pin 29 of the MCU. The signal passes through the low pass CR filter, and goes to the audio processor(IC705). The signal is mixed with the audio signal and goes to the VCO and TCXO (X1) modulation input after passing through theD/A converter inside the audio processor (IC705) for BAL adjustment.High-speed data (2-tone,DTMF)High-speed data (HSD) is output from pin 30 of the MCU. HSD deviation made by an adjustment in the MCU is passed through thelow pass CR filter and is then applied to the baseband IC (IC705).The signal is mixed with the audio signal and goes to the VCO and TCXO. The signal passes through low pass CR filter and D/Aconverter, and goes to the audio power amplifier. The level is controlled by the MCU.MSK (Fleet Sync/MDC-1200)The MSK signal is generated in the audio processor (IC705). The signal passes through the D/A converter (inside the baseband IC:IC705) and is routed to the VCO. When encoding the MSK, the microphone input signal is muted.2.1.6.2 DecodeQT/DQTThe output signal from the FM IC (IC400) enters the MCU (IC710) through IC705. IC710 determines whether or not the QT or DQTmatches the preset value, and controls the AFSW and speaker output sounds according to the squelch results.2-tonePart of the received AF signal output from the FM IC (IC400) passes through the baseband IC (IC705), and is compared beforegoing to the MCU (IC710). IC710 checks whether or not the 2-tone data is necessary. If it matches, IC710 carries out a specifiedoperation, such as turning the speaker on.MSK (Fleet Sync)The MSK input signal from the FM IC (IC400) goes to IC705. The decoded information is then processed by the MCU.DTMFThe DTMF input signal from the FM IC (IC400) goes to IC705. The decoded information is then processed by the MCU.
