RC5 coding scheme

AN2957

10/21

Doc ID 15550 Rev 2

2.4

Bit descriptions

RC5 bits are Manchester coded, this means that a bit is composed of 2 alternated half bits.

A low to high transition means that the bit is "1", a high to low transition means "0".

The frequency used to code a bit is 562.429 Hz (1778 µs), half bits have the same width

(889 µs each).

Figure 6.

RC5 bit description

2.5

RC5 frames

RC5 frames are composed of 14 bits, the width of a frame is 24.892 ms (14 x 1.778 ms =

24.892 ms)

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

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).

Figure 7.

RC5 frame description

"0"

889 µs

1778 µs

14 bits

50 bits

14 bits

Frame 1

Idle time

Frame 2

64 bits = 113.788 ms