The RC-5 code from Philips is possibly the most used protocol by
hobbyists, probably because of the wide availability of cheap remote
controls. The protocol is well defined for different device types
ensuring compatibility with your whole entertainment system. Lately
Philips started using a new protocol called RC-6 which has more features.
- 5 bit address and 6 bit command length (7 command bits for RC5X)
- Bi-phase coding (aka Manchester coding)
- Carrier frequency of 36kHz
- Constant bit time of 1.8ms
- Manufacturer Philips
The
protocol uses bi-phase modulation (or so-called Manchester coding) of a
36kHz IR carrier frequency. All bits are of equal length of 1.8ms in this
protocol, with half of the bit time filled with a burst of the 36kHz
carrier and the other half being idle. A logical zero is represented by a
burst in the first half of the bit time. A logical one is represented by a
burst in the second half of the bit time. The pulse/pause ratio of the
36kHz carrier frequency is 1/3 or 1/4 which reduces power consumption.
The drawing below shows a typical pulse train of an RC-5 message. This
example transmits command $35 to address $05.
The first two pulses are the start pulses, and are both logical "1".
Please note that half a bit time is elapsed before the receiver will
notice the real start of the message. Extended RC-5 uses only one
start bit. Bit S2 is transformed to command bit 6, providing for a total
of 7 command bits. The value of S2 must be inverted to get the 7th command
bit though!
The 3rd bit is a toggle bit. This bit is inverted every time a key is
released and pressed again. This way the receiver can distinguish between
a key that remains down, or is pressed repeatedly. The next 5 bits
represent the IR device address, which is sent with MSB first. The address
is followed by a 6 bit command, again sent with MSB first. A message
consists of a total of 14 bits, which adds up to a total duration of
25.2ms. Sometimes a message may appear to be shorter because the first
half of the start bit S1 remains idle. And if the last bit of the message
is a logic "0" the last half bit of the message is idle too.
As long as a key remains down the message will be repeated every 114ms.
The toggle bit will retain the same logical level during all of these
repeated messages. It is up to the receiver software to interpret this
auto repeat feature.
PS: I had rather a big error on this page for quite
some time. For some mysterious reason the LSB and MSB of the address and
command were reversed. I can recall correcting this error before, but
somehow an old version of the description must have sneaked its way up to
the internet again.
Philips has created a beautiful list of "standardized" commands. This
ensures the compatibility between devices from the same brand. A very
nice feature, often to be missed with other brands, is the fact that most
devices are available twice in the table allowing you to have 2 VCRs
stacked on top of each other without having trouble addressing only one of
them with your remote control. I can only show a limited list of
standard commands, for this list is about all I know right now.
RC-5 Address |
Device |
$00 - 0 |
TV1 |
$01 - 1 |
TV2 |
$02 - 2 |
Teletext |
$03 - 3 |
Video |
$04 - 4 |
LV1 |
$05 - 5 |
VCR1 |
$06 - 6 |
VCR2 |
$07 - 7 |
Experimental |
$08 - 8 |
Sat1 |
$09 - 9 |
Camera |
$0A - 10 |
Sat2 |
$0B - 11 |
|
$0C - 12 |
CDV |
$0D - 13 |
Camcorder |
$0E - 14 |
|
$0F - 15 |
|
$10 - 16 |
Pre-amp |
$11 - 17 |
Tuner |
$12 - 18 |
Recorder1 |
$13 - 19 |
Pre-amp |
$14 - 20 |
CD Player |
$15 - 21 |
Phono |
$16 - 22 |
SatA |
$17 - 23 |
Recorder2 |
$18 - 24 |
|
$19 - 25 |
|
$1A - 26 |
CDR |
$1B - 27 |
|
$1C - 28 |
|
$1D - 29 |
Lighting |
$1E - 30 |
Lighting |
$1F - 31 |
Phone | |
|
RC-5 Command |
TV Command |
VCR Command |
$00 - 0 |
0 |
0 |
$01 - 1 |
1 |
1 |
$02 - 2 |
2 |
2 |
$03 - 3 |
3 |
3 |
$04 - 4 |
4 |
4 |
$05 - 5 |
5 |
5 |
$06 - 6 |
6 |
6 |
$07 - 7 |
7 |
7 |
$08 - 8 |
8 |
8 |
$09 - 9 |
9 |
9 |
$0A - 10 |
-/-- |
-/-- |
$0C - 12 |
Standby |
Standby |
$0D - 13 |
Mute |
|
$10 - 16 |
Volume + |
|
$11 - 17 |
Volume - |
|
$12 - 18 |
Brightness + |
|
$13 - 19 |
Brightness - |
|
$20 - 32 |
Program + |
Program + |
$21 - 33 |
Program - |
Program - |
$32 - 50 |
|
Fast Rewind |
$34 - 52 |
|
Fast Forward |
$35 - 53 |
|
Play |
$36 - 54 |
|
Stop |
$37 - 55 |
|
Recording | | |