The remote codes must be analyzed by other means and saved in data files. The SIT is intended to use an asynchronous serial bitstream to modulate an infrared carrier in the simplest manner possible. It is operated exclusively from a computer. The SIT is not programmable. The codes used to control the remote equipment are stored on the computer and sent to the SIT as necessary.
Asynchronous communication is used for several reasons.
Asyn- chronous ports are available for virtually all computers. Since the asynchronous port produces a precisely timed serial bitstream, there is no need for circuitry on the SIT to do that. Also, a single byte written to the computer's serial port can be used to send several bits to the SIT, while a parallel port used for direct output would require that a byte be written for each bit to be sent. The major problem with using an asynchronous port for communication is that the infrared codes used by common equipment are not asynchronous. They are usually self-clocking bitstreams with no start or stop bits, often with variable bit timing.