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BASEBAND OVERVIEW
Issue A
Section 6
MCUK990801G8
Revision 0
– 28 –
Technical Guide
6.2.6 Real Time Clock
The Real Time Clock (RTC) and Alarm function is provided by U604 running at 32,768 MHz. It interfaces to the CPU via a four
serial lines: CE (chip enable), SCLK (serial clock), SI (serial input) and SO (serial output). To maintain power to the clock when
the main battery is removed, a small rechargeable back-up battery (VBACKUP) is used. This power source also provides power
back-up for data held in the SRAM.
The RTC can be calibrated using a high-precision oscillation adjustment function. This gives a maximum adjustment range of
±189.2 ppm in increments of 3 ppm. Addition functions of the RTC are date, alarm, periodic interrupt, 32 kHz output, supply
voltage monitoring and oscillation halt sensing.
6.2.7 Microphone
To provide improved speech pick-up, noise immunity and reduced echo, the microphone is a noise cancelling type. The GSM
standard requires that when in Handheld mode the sending audio frequency response must fit within the mask shown below.
Figure 6.4: Handheld GSM Transmit Audio frequency response mask
When using the Handsfree feature GSM requires that the sending audio frequency response must fit within the mask shown
below.
Figure 6.5: Handsfree GSM Transmit Audio frequency response mask
dB
5
-10
0
-5
-15
100
1000
10000
Frequency (Hz)
10069-1
dB
5
-10
0
-5
-15
100
1000
10000
Frequency (Hz)
10070-1
