Texas Instruments BoosterPack BOOST-IR, Руководство пользователя

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(carrier modulated pulse)
logic 1
logic 1 logic 0 logic 1
carrier
logic 1
(space)
logic 0
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3.1.1 System Design Theory
The following sections discuss the IR modulation and demodulation schemes used in this design. For
additional information about IR remote control theory and implementing IR protocols on FR4xx devices,
see the application note Infrared Remote Control Implementation with MSP430FR4xx (
SLAA644 ).
3.1.1.1 ASK Modulation
The MSP-EXP430 BOOST-IR Remote Control sends and receives ASK modulated IR signals
with a 38-kHz carrier frequency. 38 kHz is one of the most common IR carrier frequencies for remote
control applications and is used by many TV and air conditioner manufacturers.
In ASK modulation, two signals (the higher-frequency carrier, and the envelope) are combined to form the
modulated signal. The envelope contains the data to be sent, under one of many different standard
encoding schemes (for example, pulse position, pulse distance, pulse width, or Manchester encoding).
The carrier is simply a high frequency signal. When the two signals are combined, the carrier frequency is
output whenever the envelope is high, and the signal is held low when the envelope is low.
Figure 7
shows an example of an IR modulated signal using Pulse Position encoding.
Figure 7. Pulse Position Encoding (ASK)
3.1.1.2 IR Modulation Logic on MSP430FR4133
The MSP430FR4133 device includes some logic to help enable IR modulation, inside of the SYS module.
This logic block allows the outputs signals from some timer modules in the device (producing the carrier
frequency) to be combined with an envelope generated by another timer module, the output of the
USCI_A0 module, or with a software controlled IRDATA line. In addition, the Timers can optionally be
cascaded. TA1 can select to use TA0 as the clock source so that TA1 is essentially counting ticks of the
TA0 PWM output signal. This arrangement allows for flexible and configurable generation of all different
kinds of ASK and FSK modulation schemes.
Figure 8 shows an overview of the modules involved in
internal IR signal generation on the FR4133.
11 SLAU598A – December 2014 – Revised July 2015 BOOST-IR Infrared (IR) BoosterPack™ Plug-in Module
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