Southern Avionics Company SD100 Manual Do Utilizador
SD SERIES TRANSMITTER
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Southern Avionics Company
2.2.4 Digital I/O and PWM PCB
SLP10009 Digital I/O and PWM Theory
The Digital I/O and PWM PCB consists of several sub sections which accomplish the following functions:
Digital Input State Reading
Digital Output Control
Frequency Counting
Audio to PWM Conversion
AWOS Option.
Digital Output Control
Frequency Counting
Audio to PWM Conversion
AWOS Option.
The Digital Input Section receives and conditions state information from the various system modules mainly
indicating the fault status of these sections but also monitoring the state of other sensors. While retaining their unique
state value all of these signals are combined into one interrupt request (IRQ) line for rapid servicing of external
events. A local red fault LED indicates the arrival of a fault condition. The processor take action depending on the
nature of the condition.
state value all of these signals are combined into one interrupt request (IRQ) line for rapid servicing of external
events. A local red fault LED indicates the arrival of a fault condition. The processor take action depending on the
nature of the condition.
The Digital Output Section conditions and outputs a state condition to the various system modules primarily
to perform fault resets. Antenna switching is also controlled by this section.
The Frequency Counter section conditions and samples the Direct Digital Synthesizer generated frequency
from the RF power amplifier. This data is relayed to the processor which monitors the output RF frequency for
accuracy.
accuracy.
The PWM section of this board inputs audio signals from the tone generating Direct Digital Synthesizer and
from an optional voice input piggybacked PCB for AWOS functionality. The composite audio signal is summed with
an adjustable DC level and converted into a 75 kHz Pulse Width Modulated signal with its basic no-audio duty cycle
being set at a fixed percentage. This fixed level facilitates modulation tracking irregardless of power level output. A
back-up modulation limiting circuit prevents over-modulation from damaging the RF Amplifier but main over
modulation protection control for Tone signals is a software function of the processor which monitors modulation at
all times.
an adjustable DC level and converted into a 75 kHz Pulse Width Modulated signal with its basic no-audio duty cycle
being set at a fixed percentage. This fixed level facilitates modulation tracking irregardless of power level output. A
back-up modulation limiting circuit prevents over-modulation from damaging the RF Amplifier but main over
modulation protection control for Tone signals is a software function of the processor which monitors modulation at
all times.
The Optional AWOS plug in PCB Contains an AGC section which prevents over-modulation by the USER
audio signal. There is also a built in active Audio band-pass filter which eliminates signals outside of the 300 to
3000Hz pass band. Signals generated on this Optional PCB also alert the processor which then cuts the main tone
level and temporarily ceases issuing any modulation alarms based on modulation percentage.
3000Hz pass band. Signals generated on this Optional PCB also alert the processor which then cuts the main tone
level and temporarily ceases issuing any modulation alarms based on modulation percentage.