RC5 Protocol is a standard infrared data communication protocol used in remotes. This protocol was developed by Philips. It has 2048 different commands which are divided into 32 addresses each of 64 commands.

RC5 standard uses fix bit length & fixed number of bits. It uses bi phase modulation technique  i.e. each bit  consists of two part & has a level transition (high to low or low to high). A '1' is defined by low to high transition & a '0' is defined by high to low transition. The duration of each bit is equal to 1.778ms since the RC5 protocol consists of 14 bits so the total duration is approximately 24.8ms. The carrier frequency used for transmitting is 36KHz.

RC5 Bit Logic

RC5 Bit Logic
As stated earlier this protocol consists of 14 bits as follows:

RC5 Protocol

The first two bits are the start bits used for Automatic Gain Calibration (AGC) of the receiver. These are basically two HIGH bits.

The third bit is TOGGLE BIT or CHECK BIT,  this bit toggles every time a new button is pressed.

The next 5 bits ADDRESS BITS each device has a specific address. This is used to identify which kind of device executes the command bits.

The next 6 bits are COMMAND BITS. These bits are used to give instruction to the addressed device i.e. what action to perform.

Since the carrier frequency of the RC5 code is 36 KHz we require a receiver with a response frequency of 36KHz. one such receiver is VISHAY's TSOP1836. It is basically a 3 pin device & gives demodulated output signal which can directly be decoded by the microcontroller.