User Guide

PAMS
Technical Documentation
NSB–1
System Module
Original 06/98
Page 3 – 22
Speech processing
The speech coding functions are performed by the DSP in the MAD and
the coded speech blocks are transferred to the COBBA for digital to ana-
log conversion, down link direction. In the up link direction the PCM coded
speech blocks are read from the COBBA by the DSP.
There are two separate interfaces between MAD and COBBA: a parallel
bus and a serial bus. The parallel bus has 12 data bits, 4 address bits,
read and write strobes and a data available strobe. The parallel interface
is used to transfer all the COBBA control information (both the RFI part
and the audio part) and the transmit and receive samples. The serial in-
terface between MAD and COBBa includes transmit and receive data,
clock and frame synchronization signals. It is used to transfer the PCM
samples. The frame synchronization frequency is 8 kHz which indicates
the rate of the PCM samples and the clock frequency is 1 MHz. COBBA is
generating both clocks.
Alert Signal Generation
A buzzer is used for giving alerting tones and/or melodies as a signal of
an incoming call. Also key press and user function response beeps are
generated with the buzzer. The buzzer is controlled with a BuzzerPWM
output signal from the MAD. A dynamic type of buzzer must be used
since the supply voltage available can not produce the required sound
pressure for a piezo type buzzer. The low impedance buzzer is connected
to an output transistor that gets drive current from the PWM output. The
alert volume can be adjusted either by changing the pulse width causing
the level to change or by changing the frequency to utilize the resonance
frequency range of the buzzer.
A vibra alerting device is used for giving silent signal to the user of an in-
coming call. The device is controlled with a VibraPWM output signal from
the MAD. The vibra alert can be adjusted either by changing the pulse
width or by changing the pulse frequency. The vibra device is not inside
the phone, but in a special vibra battery.