【正文】 tion, the PIC16C57 resets.Upon startup a “hyphen”will be displayed in the left digit space until the infrared input settles to the dark logic indicating that the unit is ready to receive an infrared signal.As an infrared signal es in, the lengths of bursts of infrared, and the lengths of gaps between burst are stored in consecutive file locations until all four pages of the PIC16C57’s memory files are filled. If a jumper had been in 1, the program throws away the first 32 pulse and gap lengths and starts storing pulse and gap lengths with the thirty third pulse length. This allows the decoding of very long formats.When all four pages of file memory are filled with pulse and gap lengths, a number and decimal point are displayed. The decimal point indicates that the unit is donereading. The number is a gap or pulse and SW3 control the time sequence of the pulse or gap length displayed. These are in octal with SW3 being the more significant digit.INSTRUCTIONS ON WRITING AN ALGORITHM TO DECODE IR REMOTES1. To design a system that uses an infrared remote control, the first step is to choose a remote control. Self designed or off the shelf, modulated or unmodulated are the primary technical decisions. 2. Once a remote control has been chosen or designed, its modulation frequency, if it has one, must be determined. This controls the kind of hardware used to receive the infrared signal. 3. The next step is to determine the timebase of the data, that is, if the pulses and gaps are short or long in reference to the PIC16C57 clock. The OPTION switch, SW1, is used to get optimum length pulse and gap counts from TMR0. This defines the value of the OPTION prescaler. 4. Fourth, definition is made as to what, in the format, defines a 39。, a short gap or burst is interpreted as a 39。7Decoding Infrared Remote Controls Using a PIC16C5X MicrocontrollerINTRODUCTIONFor many years the consumer electronics industry has been employing infrared remote controls for the control of televisions, VCR’s, and cable boxes. This same technology has recently started to appear in industrial applications to eliminate keypads.Decoding most of the infrared signals can be easily handled by PIC16C5X microcontrollers. This application note describes how this decoding may be done.The only mandatory hardware for decoding IR signals is an infrared receiver. The use of two types is described here. Both are modular types used often by the consumer electronics industry. The ?rst type responds to infrared signals modulated at about 40 kHz. The second responds to nonmodulated infrared pulses and has a restricted range. The hardware costs of each approach will be less than two dollars. Three PIC16C5X application programs are described, and instructions on how they can be used to create an algorithm that can decode just about any remote control signal. Each PIC16C5X application program represents a step in mapping out a preexisting infrared format. The ?nal application is a fully implemented example of decoding and interpreting the infrared signals of a type of Teknika TV remoteTHE THREE LAYERS OF AN INFRARED SIGNALThe typical infrared signal used by remote controls has three layers. The names used for these layers has not been standardized. In this application note they are called the infrared, the modulation, and the serial data.The infrared layer is the means of transmission. Infrared is light whose wavelength is too long to see. Although you cannot see the infrared beam, it behaves the same as light, so if you cannot see the target device, you cannot control it with an infrared signal. To control around corners or through opaque materials, RF, usually UHF signals are used. Although this application note does not further mention RF, much of what is presented here can be used with an RF transmission medium.The modulation layer refers to the fact that each burst of infrared signal is often modulated at a frequency between kHz and kHz. This is done to diminish the effects of ambient light. This layer, however, is optional. Some infrared formats do not modulate their outputs, send