What is the RC 5 protocol

RC5 (decoding with PIC microcontroller, electronics)

1. RC5 protocol

The RC5 code was developed by Philips and is a very widespread standard for infrared data transmission in Europe. It is very often used with infrared remote controls.

In the idle state, i.e. when no key is pressed, the level is low. When a button is pressed, a 24.889ms long code is sent. This code is repeated as often as long as the key is kept pressed, with a pause of 88.889ms in between (following picture above).

The RC5 code is coded biphase. This meant that a bit is composed of two alternating half bits. In other words, this means that a logic “1” consists of a low-high transition and a logic “0” consists of a high-low transition. (following picture middle and bottom).

The transmitted code consists of a 14-bit long data word (see above figure in the middle) and is structured as follows.

  • 2 start bits
  • 1 toggle bit
  • 5 system address bits
  • 6 command bits

The two start bits are used to set the so-called auto gain control (AGC) in the receiver IC.

The toggle bit changes its state each time a button is pressed. This allows a distinction to be made between pressing the same key continuously and pressing the same key several times.
The system address bits indicate which device (TV1, video recorder, etc.) is to be addressed by the remote control. The following table shows the assignment between device and system address according to Philips. The system address is decimally coded in this table.

Addr. Device addr.

Addresses 7 and 13 are intended for DIY devices and for experimentation purposes.

The command bits indicate which key on the remote control was pressed. The following table shows the commands that apply to all addresses.

Command button on the command button on the remote control Remote control ---------------------------------------- ----------------------------------------- 0 0 18 Brightness + 1 1 19 Brightness - 2 2 20 Color saturation + 3 3 21 Color saturation - 4 4 22 Bass + 5 5 23 Bass - 6 6 24 Treble + 7 7 25 Treble - 8 8 26 Balance right 9 9 27 Balance left 16 Volume + 63 System select 17 Volume -

Author: Buchgeher Stefan
Created: July 5, 2004
Last change: September 29, 2004