T9000
Preliminary Data Sheet
November 2000
ISDN Network Termination Node (NTN) Device
12 PWM Module
The PWM module is comprised of a general-purpose dual pulse-width modulator with sine modulation capability.
Each module is capable of generating a sequence of pulses of programmable width and period. The generated
pulses are centered in the programmed period. Figure 21 illustrates a general case of the PWM output signal for
the two PWM generators. Normally, the pulse period is determined ahead of time and does not change during the
pulse train generation. Pulse-width values change according to the user’s desired algorithm.
In POTS applications, pulse-width modulated signals are typically used for generation of:
■ Call alert signals (20 Hz to 30 Hz typical)
■ Billing signals (50 Hz and 12 kHz typical)
■ Answering machine control signals (2 kHz typical)
■ Identification tones (697 Hz to 2 kHz)
In these applications, the width of the PWM signal is modulated according to the amplitude of a sine wave sampled
at pulse period intervals. The PWM signal is then low-pass filtered with a simple RC integrator.
There are three configuration registers per PWM generator: PWxCF, PWxVH, and PWxVL, where x = 0 or 1. In
addition, there is a common PWM interrupt register (PWIR) shared by both generators. Both generators are identi-
cal, so references to these registers in the explanation that follows will simply use x in place of 0 or 1 in the register
names.
Each PWM output can be made available on two separate GPIO pins according to the programming of register bits
GPAF0.[7:4]. This allows the same PWMO to drive two different external devices by proper programming of regis-
ter GPAF0.[7:4]. For example, the outputs of PWMO (PWMO00 and PWMO01) can drive two external devices and
the outputs of PWM1 (PWMO10 and PWMO11) can also drive 2 different external devices.
PWM
SEE DETAIL BELOW
RANGE × TICK
RANGE × TICK
RANGE × TICK
PWM
PW
PW
5-6522F
Figure 21. Pulse-Width Modulated Output Signal
Lucent Technologies Inc.
93
AGERE [ AGERE SYSTEMS ]
