Phillips RC5 infrared remote protocol page



Most audio and video systems are equipped with an infrared remote control. A common used standard protocol for infrared data communication is the RC5 code, originally developed by Phillips. This code has an instruction set of 2048 different instructions and is divided into 32 address of each 64 instructions. Every kind of equipment use his own address,so this makes it possible to change the volume of the TV without change the volume of the hifi. The transmitted code is a dataword wich consists of 14 bits and is defined as:

2 startbits for the automatic gain control in the infrared receiver.
1 toggle bit (change everytime when a new button is pressed on the ir transmitter)
5 address bits for the systemaddress
6 instructionbits for the pressed key

The picture under are waveforms from my digital oscilloscope of rc5 codes with pushed buttons 1,2,3,4. You can good see the startbits and the toggle bit (These are inverted signals because they were captured directly on the TSOP1836). Read further for more info.


 
The RC5 code uses the bifase modulation technic which means that every bit consists of 2 parts which are never the same.
So a bit is always a high/low or a low/high transisition. By the RC5 code a 1 is a low high transisition
and a 0 is high low transisition. For all the bits the most significant bit is transmitted first.
Remember also that the outputsignal of the integrated receivers is inverted:
Detecting an IR signal the output of the integrated receiver will be 0V.
The duration time of each bit is equal to 1,778 ms, and the total time of a full rc5 code is 24,778 ms.
The space between two transmitted codes is 50 bit times or 88,889ms.
To improve noise rejection the pulses are modulated at a carrier frequence
The carrier frequency of the rc5 code is 36 kHz so take always a receiver with a response
frequency of 36 kHz.
There are plenty of Detectors for receiving the bitstream of an IR remote control but the best
I ever used is the TSOP1836 of VISHAY. (Datasheet available on my site).

The TSOP1836 is a 3 pin device that receives the infrared bursts and gives out the demodulated bitstream at the output. The RC5 code is an easy protocol to decode with a pic mircrocontroller . I will show an example to control your PC when it's finished
Find more information on my other pages

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