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14
1.1.8. Modem and Peripheral Circuit (Optional FXB PCB)
This circuit consists of DSP, ROM, S-RAM, Analog Front End, Analog Master and peripheral circuitry.
This modem conforms to ITU-T, V.34, V.33, V.17, V.29, V.27ter, V.21 channel 2 (FSK), T.4, and T.30.
Macro order of DSP is sent from ROM to S-RAM and is outputted. DSP transfers/receives data from
Analog Front End and serial communication. Analog Front End communicates with the line through
Analog Master.
To Line
To Speaker
Analog
Master
Analog
Front
End
DSP
IC901
Modem
CPU
Modem
CPU
IC906
IC904
IC902
IC905
S-RAM
ROM
Modem
Program
Program
System BUS
Modem Circuit Block Diagram
1. Receive Signal Control Circuit
This circuit consists of Operational Amplifier, Analog Master, and its peripheral circuit. On the received
signal from a line transformer (HYBSR), diffraction of signal transmission is attenuated using the
hybrid circuit, and the frequency of signal is limited to a certain band using a second LPF.
The signal is input to the analog front end via the analog SW for switching over between HYSIG and
the gain switching amplifier. 1300-Hz signal and remote signal are detected from HYSIG by switching
SW1.
2. Transmission Signal Control Circuit
This circuit consists of Operational Amplifier, Analog Master, and its peripheral circuit. On the signal
transmission from the analog front end, frequency of the signal is limited to a certain band using a
second LPF, and diffraction of the signal to a reception circuit is attenuated using the hybrid circuit.
The signal is sent out from the line transformer.
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