AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 22

• Manufacturer Part Number: AN1833
• Description: A Low-Power Wireless Remote Control Transmitter and Receiver
• Manufacturer: Freescale Semiconductor / Motorola

Application Note
MCU Introduction
Microcontroller Software Overview: Initiate an Access Request
Interrupt Service
Routine
22
A low-power wireless remote control system has four pieces:
The microcontroller unit (MCU) in the remote control unit decodes the
button that has been pressed and sends a bitstream to an RF
transmitter. The receiver acquires the RF bitstream, converts it to digital
format for an MCU, which analyzes the digital data, and determines what
operation is to be performed.
A battery-powered remote control unit waits in an extremely low-power
or sleep mode until someone presses a button or series of buttons on
the unit. (Low-power mode means a battery will power the unit longer.)
Pressing buttons causes the MCU to wake up and begin executing an
internal sequence of commands that determine what keys have been
pressed. The MCU in this design is an MC68HC705J1A [5]. The
keystrokes are stored by the MCU and determine the format of an
access request message.
When a keypad button is pressed, it asserts an input pin that triggers the
execution of the interrupt service routine (ISR). The MCU clock feeding
the MC13176 turns on when a keypad button is depressed. Decoding of
which key is depressed is done using the routines written by David
Yoder [12]. The ISR examines the port A input values when certain
port B outputs are asserted.
1. Method of initiating a request such as a button on a remote control
2. Sending a message from an RF transmitter
3. Receiving and validating a message
4. Determining action to be taken such as releasing a solenoid or
Freescale Semiconductor, Inc.
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unit
turning on a light
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MOTOROLA
AN1833