NEC 红外遥控协议_红外pulsedistance协议

NEC Protocol

原文地址:

http://www.sbprojects.com/knowledge/ir/nec.php

To my knowledge the protocol I describe here was developedby NEC. I've seen very similar protocol descriptions on the internet, and therethe protocol is called Japanese Format.
I do admit that I don't know exactly who developed it. What I do know is thatit is used in my late VCR produced by Sanyo and was marketed under the name ofFisher. NEC manufactured the remote control IC.
This description was taken from the VCR's 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 1.125ms or 2.25ms

Modulation

The NEC protocol uses pulse distance encoding of thebits. Each pulse is a 560µs long 38kHz carrier burst (about 21 cycles). Alogical "1" takes 2.25ms to transmit, while a logical "0"is only half of that, being 1.125ms. The recommended carrier duty-cycle is 1/4or 1/3.

Protocol

The picture above shows a typical pulse train of the NECprotocol. 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 isthen followed by a 4.5ms space, which is then followed by the Address andCommand. Address and Command are transmitted twice. The second time all bitsare inverted and can be used for verification of the received message. Thetotal transmission time is constant because every bit is repeated with itsinverted length. If you're not interested in this reliability you can ignorethe inverted values, or you can expand the Address and Command to 16 bits each!

A command is transmitted only once, even when the key onthe remote control remains pressed. Every 110ms a repeat code is transmittedfor as long as the key remains down. This repeat code is simply a 9ms AGC pulsefollowed by a 2.25ms space and a 560µs burst.

Extended NEC protocol

The NEC protocol is so widely used that soon all possibleaddresses were used up. By sacrificing the address redundancy the address rangewas extended from 256 possible values to approximately 65000 different values.This way the address range was extended from 8 bits to 16 bits without changingany other property of the protocol.
The command redundancy is still preserved. Therefore each address can stillhandle 256 different commands.

Keep in mind that 256 address values of the extendedprotocol are invalid because they are in fact normal NEC protocol addresses.Whenever the low byte is the exact inverse of the high byte it is not a validextended address.

External Links

NECElectronics

Example Commands

The table below lists the messages sent by the remotecontrol of my late Fisher 530 VCR (it served us well during its 20 years longlife).