UM1546

System overview

Doc ID 023229 Rev 1

7/17

Figure 3.

RC5 bit representation

The RC5 frame can generate 2048 (32x64) different commands organized in 32 groups,

each group has 64 different commands. An RC5 frame contains the following fields (an

example of an RC5 frame is shown in Figure 2):

●

Start bit (S): 1 bit length, always logic 1.

●

Field bit (F): 1 bit length, which denotes whether the command sent is in the lower field

(logic 1 = 0 to 63 decimal) or the upper field (logic 0 = 64 to 127 decimal).

●

Control bit or Toggle bit (C): 1 bit length, which toggles each time a button is pressed.

This allows the receiving device to distinguish between two successive button presses

(such as “1”, “1” for “11”).

●

Address: 5-bit length that selects one of 32 possible systems.

●

Command: 6-bit length, that (in conjunction with the field bit) represents one of the 128

possible RC-5 commands.

Figure 4.

Example of an RC5 frame

To avoid frame collisions, an idle time is inserted between two frames with a specific width

(see Figure 3).

The idle time is defined as 50 bits wide. So the periodicity of a frame is 64 x 1 bit width:

64 x 1.778 = 113.792 ms (exactly 113.788 ms).

AM12357v1

Modulated RC5 bit

Demodulated RC5 bit

Logic ‘0’

Logic ‘1’

889 µs889 µs

889 µs

889 µs

AM12343v1

Address = 4

Command = 39

Field bit = 1 (Command 0-63)

Control bit = 0

S F

5 x Address bits

6 x Command bits

11

1

1

1

C