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| Philips RC-5 Protocol |
The RC5 code from Philips is probably the most used protocol by
hobbyists, probably because 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 RC6 which has more features.
| Features |
- 5 bit address and 6 bit command length
- Bi-phase coding (aka Manchester coding)
- Carrier frequency of 36kHz
- Bit time of 1.8ms
- Manufacturer Philips
| Modulation |
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,
to reduce power consumption.
| Protocol |
The drawing below shows a typical pulse train of an RC5 message. This
example transmits command $2B to address $14. 
The first two pulses are the
start pulses, and are both logic "1". Please note that the half a bit time
is elapsed before the receiver will notice the real start of the message.
Extended RC5 uses only one start bit. Bit S2 will is transformed to
command bit 6, providing for a total of 7 command bits.
The 3d bit
is a toggle bit. This bit is inverted every time a key is pressed. This
way the receiver can distinguish between a key that remains down, or
pressed repeatedly.
The next 5 bits represent the IR device address,
which is sent with LSB first. The address is followed by a 6 bit command.
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 remain the same during all of these messages.
It is up to the receiver software to interpret this auto repeat feature.
| Pre-defined Commands |
Philips has created a beautiful list of "standardised" commands. This
ensures the compatibility between devises 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.
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