1. Field of the Invention
The invention relates to a decoding circuit and a decoding method thereof, and more particularly, to a decoding circuit of a DMX512 signal format and a decoding method thereof.
2. Description of Related Art
DMX512 protocol standard is a data transmission standard initially proposed by United States of Institutes for Theater Technology (USITT) in 1986, and is a commonly used control protocol in the field of entertainment lighting. The DMX512 communication technology applies an asynchronous communication format, where each lighting adjustment data is composed of 11 bits, including one bit representing a start time, 8 bits representing a data byte and two stopping bits, and 512 lighting adjustment data can be transmitted every time. Currently, stage light controls mostly use the DMX512 protocol standard to perform the stage light control.
In the DMX512 protocol standard, every transmitting data includes a break signal and a plurality of data signals, where the break signal is usually a logic low level for 88 micro-seconds(μs). The break signal is a start signal of data, and a chip can determine a start of the signal by detecting the break signal. The break signal is followed by a plurality of time slots, and there is also a mark between every neighboring time slots as an interval, where the mark is a logic high level. When there is no DMX data packet generated, the signal is kept at the logic high level, and this is a mark after the last time slot. Therefore, there is usually a mark signal of the logic high level present before the break signal.
Nowadays, the driver circuit of light emitting diodes (LED) may also apply the DMX 512 signal format to transmit the driving data. In order to speed up the data transmission, transmission ways of 2 frequency multiplications (or two times the frequency of an standard DMX 512 protocol) or 4 frequency multiplications (or four times the frequency of an standard DMX 512 protocol) of the standard DMX512 signal format transmission rate are applied, mainly to shorten the standard time specification in the DMX512 signal format to ½ or ¼. Since the driver circuit of LED usually transfers the DMX512 signals in a serially connected fashion, if there are too many of the serially connected chips, the signal is easily made distorted, and the chip(s) serially connected thereafter thereby cannot correctly decode the data.