1 RC5 Coding Scheme

The RC5 code is a 14-bit word bi-phase coded signal as seen in the figure below. The first two bits are start bits, always having the value “1”. The next bit is a control bit, which is toggled every time a button is pressed on the remote control transmitter. This gives an easy way of determining whether a button is pressed and held down, or pressed and released continuously.

Figure 1-1. RC5 Frame Format

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 below, along with an example where the command 0x35 is sent to system 5.

Figure 1-2. Bi-phase Coding
Figure 1-3. Example of Transmission

Note that the figures above show the signal that enters the Atmel ATtiny28 hardware modulator. The actual signal emitted by the IR-LED will be modulated with a certain carrier frequency as shown in the figure below.

Figure 1-4. Signal Before and After Modulation