Supply Voltage Measurement
The supply voltage is measured using MCU N420 A/D converter channel 0. The supply voltage supplied to the A/D converter input is switched off when the baseband is powered off. The supply voltage measurement voltage is supplied by PSCLD N300, which performs switch-off, and scaling with a scaling factor of R1(R1+R2). The measurement voltage is Filterered by a capacitor to achieve an average value that is not depending upon the current consumption behavior of the baseband. To be able to measure the supply voltage during transmission pulse, the time constant must be short. The value for the Filterering capacitor is set to 10 nF C316. The scaling factor used to scale the supply voltage must be 1:3, which means that a 9V supply voltage will give 3V A/D converter input voltage. The A/D converter value in decimal can be calculated using the following formula:
A/D = 1023xR1xUBAT/((R1+R2)xUref) = 1023xUbatxK where K is the scaling factor. K = R1/((R1+R2)xUref).
Technical Documentation System Module
The audio codec N130 is controlled by the MCU D420. The ASIC generates a 512 kHz data clock, and a 8 kHz synchronization signal for the PCM data bus. Data is put out on the bus at the rising edge of the clock and read in at the falling edge. Data from the DSP D360 to the audio codec N130 is transmitted as a separate signal from data transmitted from the audio codec, N130 to the DSP D360. The communication is full duplex synchronous. The transmission is started at the falling edge of the synchronization pulse. 16 bits of data is transmitted after each synchronization pulse.
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