Protocol Packets

Before you begin to describe the structure of the package DMX512, I want to mention that I assume the existence of the reader's basic knowledge about the provision of data in digital form. Data in the DMX512 is a set of high (HI) and low (LO) signal levels, which represent 1 and 0 respectively.

DMX512 protocol operates at a frequency of 250 kHz - which means that each bit has a duration of 4 microseconds.

Standby (Idle), or NO DMX

If you do not correctly render DMX packet to the output DMX line will be a constant high level signal (HI, 1).

Reset (Break)

Length not less than 88 microseconds. This means that transferred 22 of zero (LO) bit of one another. Such a sequence is called a reset command (Break). Its duration may be longer and reach 1 with.

Practice shows that a little more long reset signals (slightly more than 88 microseconds) are recognized better as devices are usually programmed by the following algorithm: Break = 88 microseconds, or 22 pulse.

I believe that the optimal duration is 120 microseconds.

Tag after Reset (Mark After Break (MAB)

Tag after Reset (MAV) is transmitted immediately after the Break and a high level signal (HI) for a minimum period of 8 microseconds, or 2 pulse. With this signal there are some problems because of the difference of the initial standard DMX512 and DMX512 (1990), which is currently used. In the original version of the duration of this signal was equal to 1 pulse or 4 microseconds. This caused failures in some host devices, since the signal was too short to detect, and in 1990 increased the duration of the MAV to 8 microseconds, or 2 pulses. This causes some difficulties when using old consoles to new devices and vice versa. Incorrect recognition MAV distorts the interpretation of the package and hit the "wrong" information in the "wrong" channel. This error will be distributed along the line, yet not lead to complete disorder. Some devices have a dip-switch, with which you can set time parameters of these signals. Maximum length of the signal MAV can be 1 to. From myself I can advise the option in 12 microseconds as the ideal.