Avr411

AVR410: RC5 IR Remote Control Receiver
Features
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Low-cost Compact Design, Only One External Component Requires Only One Controller Pin, Any AVR Device Can be Used Size-efficient Code

8-bit Microcontroller Application Note

Introduction
Most audio and video systems are equipped with an infrared remote control. This application note describes a receiver for the frequently used Philips/Sony RC5 coding scheme. Figure 1. RC5 Receiver

DATA

The RC5 code is a 14-bit word bi-phase coded signal (See Figure 2). The two first bits are start bits, always having the value one. The next bit is a control bit or toggle bit, which is inverted every time a button is pressed on the remote control transmitter. Five system bits hold the system address so that only the right system responds to the code. Usually, TV sets have the system address 0, VCRs the address 5 and so on. The command sequence is six bits long, allowing up to 64 different commands per address. The bits are transmitted in bi-phase code (also known as Manchester code) as shown in Figure 3. An example where the command 0x35 is sent to system 5 is shown in Figure 4.

Rev. 1473B–AVR–05/02

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Figure 2. RC5 Frame Format

Figure 3. Bi-phase Coding

Figure 4. Example of Transmission

Timing

The bit length is approximately 1.8 ms. The code is repeated every 114 ms. To improve noise rejection, the pulses are modulated at 36 kHz. The easiest way to receive these pulses is to use an integrated IR-receiver/demodulator like the Siemens SFH 506-36. This is a 3-pin device that receives the infra-red burst and gives out the demodulated bit stream at the output pin. Note that the data is inverted compared to the transmitted data (i.e., the data is idle high). The assembly code found in AVR410.ASM contains the RC5 decode routine. In addition, it contains an example program which initializes the resources, decodes the RC5 data and outputs the received command on port B. When the detect subroutine is...