Dell 2145cn Service Manual page 38

Product spec and feature
Signal Transition of DAA Solution
Line Interface Signal of Tel Line and LSD is Analog Signal. There are a A/D and a D/A Converter in the LSD,
so Analog Signal from Tel Line is converted in Digital through a A/D Converter in the DAA and transferred to
the SSD by the DIB Transformer. Digital Signal from the SSD is converted to Analog by a D/A Converter in
the DAA and transferred to Tel Line.
( Modem ) ( Silicon DAA )
1) Modem Side
The Si2435 modem device contains a controller, a DSP, program memory (ROM), data memory (RAM), a
serial and parallel interface, a crystal oscillator, and an isolation capacitor interface.
The crystal oscillator circuit requires a 4.9152MHzfundamental mode parallel-resonant crystal. Typical
crystals require a 20pF load capacitance. This load is calculated as the series combination of the
capacitance.
Frequency stability and accuracy are critically important to the performance of the modem. ITU-T
specifications require less than 200ppm difference in the carrier frequency of two modems.
In the system there are two system interface options, serial and parallel. The serial interface allows the host
processor to communicate with the modem controller through a UART driver. The system is adopted UART
interface.
2) DAA Side
The Si3018, DAA or line-side device, contains an ADC, a DAC, control circuitry, and an isolation capacitor
interface. The Si3018 and surrounding circuitry provide all functionality for telephone line interface
requirement
compliance including a full-wave bridge, hook switch, dc termination, ac termination, ring detect, loop
voltage/current monitoring, and call progress monitoring.
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