The SIRC protocol uses a pulse width encoding of the bits. The pulse representing a logical "1" is a 1.2ms long burst of the 40kHz carrier, while the burst width for a logical "0" is 0.6ms long. All bursts are separated by a 0.6ms long space interval. The recommended carrier duty-cycle is 1/4 or 1/3. With this protocol the LSB is transmitted first. The start burst is always 2.4ms wide, followed by a standard space of 0.6ms. Apart from signalling the start of a SIRC message this start burst is also used to adjust the gain of the IR receiver. Then the 7-bit Command is transmitted, followed by the 5-bit Device address. Commands are repeated every 45ms(measured from start to start) for as long as the key on the remote control is held down. #1200 _600 #600 _600 #2400 _600 The NEC protocol uses pulse distance encoding of the bits. Each pulse is a 560us long 38kHz carrier burst (about 21 cycles). A logical "1" takes 2.25ms to transmit, while a logical "0" is only half of that, being 1.125ms. The recommended carrier duty-cycle is 1/4 or 1/3. A message is started by a 9ms AGC burst, which was used to set the gain of the earlier IR receivers. This AGC burst is then followed by a 4.5ms space, which is then followed by the Address and Command. Address and Command are transmitted twice. The second time all bits are inverted and can be used for verification of the received message. The total transmission time is constant because every bit is repeated with its inverted length. If you're not interested in this reliability you can ignore the inverted values, or you can expand the Address and Command to 16 bits each! #560 _1690 #560 _560 #9000 _4500 #560 A command is transmitted only once, even when the key on the remote control remains pressed. Every 110ms a repeat code is transmitted for as long as the key remains down. This repeat code is simply a 9ms AGC pulse followed by a 2.25ms space and a 560us burst #9000 _2250 #560 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. The protocol uses bi-phase modulation (or so-called Manchester coding) of a 36kHz IR carrier frequency. All bits are of equal length of 1.778ms 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 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. 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 ms. 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. _889 #889 #889 _889 #889 _889 #889 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! _889 #889 #889 _889 #889 Protocol used in Panasonic DVD players and TVs. I didn't find any description of this protocol, so I made it up by myself. Bear in mind that data may be coded differently! #440 _1300 #440 _440 #3500 _1700 #440 Silverlit PicoZ remote control. #1250 _1200 #650 _600 #600 _600 #1250 _2979 #1950 _600 #650 24 bit Protocol used in RCA sound systems. It looks similar to NEC. (38 khz) I didn't find any description of this protocol, so I made it up by myself. Bear in mind that data may be coded differently! --Chad Carisch #562 _1937 #562 _937 #4062 _3937 #562