红外编码格式3—NECProtocol定义.pdf

[ 编码资料 ] 红外编码格式 3 —NEC Protocol NEC Protocol To my knowledge the protocol I describe here was developed by NEC. Ive seen very similar protocol descriptions on the internet, and there the protocol is called Japanese Format. I do admit that I dont know exactly who developed it. What I do know is that it is used in my late VCR produced by Sanyo and was marketed under the name of Fisher. NEC manufactured the remote control IC. This description was taken from the VCRs service manual. Those were the days, when service manuals were fulled with useful information! Features 8 bit address and 8 bit command length Address and command are transmitted twice for reliability Pulse distance modulation Carrier frequency of 38kHz Bit time of 1.12ms or 2.25ms Modulation The NEC protocol uses pulse distance encoding of the bits. Each pulse is a 560 μs long 38kHz carrier burst (about 21 cycles). A logical 1 takes 2.25ms to transmit, while a logical 0 is only 1.12ms. The recommended carrier duty-cycle is 1/4 or 1/3. Protocol The picture above shows a typical pulse train of the NEC protocol. With this protocol the LSB is transmitted first. In this case Address $59 and Command $16 is transmitted. 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 u