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Other Protocol Packets

Start Code (Start Code (SC)

Next in order is a signal SC. The easiest way to remember that the start code (SC) - this is the beginning of the current data stream in which the data of each channel have the same format. Break and MAB are different from other frames, but start code (SC), prior to all personnel must have with them the same structure and length of 11 pulses, or 44 microseconds. The first frame can be called the data for the channel to number 0, which in principle does not exist, but it is precisely SC. To begin, consider the structure of data frames. The first of 11 pulses is always 0 (LO) and represents the start bit. After it is very data bytes of 8 bits (which can take values from 0 to 255 (28-1). Kadr ends two unit (HI) bits, which are the stop and mark the end of the data for this channel. Chat room 0 - this is SC that, in general, always has zero bytes of data, thereby showing that enables the transfer of data to dimmers. According to the current standard of no other value can not be used. Sometimes, though, SC is used to transfer the receiver of information that the next packet is specific type of receivers. Actually, this is one of the key appointments SC - separate data packets, depending on the receiver. But to date, according to the standard data byte SC should have a value of 0, which is reserved for the dimmers. It must be remembered that this concept is incorporated almost all instruments: dimmers, scanners, and so on.!

Tag Time between frames (Mark Time Between Frames (MTBF)

Check the time between shots can be from 0 to 1 second, but less is better. In each frame is MTBF, which precedes the start-bit and shared pictures of one another. MTBF is 1 (HI).

Data Channel (Channel Data (CD)

Personnel channel data followed by frame SC order from 1 to 512 (or less) and have the format described above.

Tag Time between packets (Mark Time Between Packets (MTBP)

Once sent to the last stop bit of the data channel (CD), can begin transmission of a new package by sending a header Reset + mark after reset "(Break + MAB). At this point, as a rule, insert a short period of inactivity (IDLE), which represents a high level signal and in this case is called MTBP. This signal can be from 0 to 1 second, and each developer chooses this option to ensure optimal performance.


The most remarkable in the DMX512 is that there is no need to transmit Channel Number!

The first byte of data after the startup code (which is always 0) is automatically taken as data for the first channel, the next - for the second, the next one - for the third and so on up to 512 or fewer channels. Here's how the receiver interprets the transmitted data signals, be it a scanner, a rotating head or dimmer. At the receiver, and has a meter channels, built into the microprocessor, or implemented as a separate unit. This counter is reset to 0 when the receiver receives a combination of "Reset + Tag after Reset" (Break + MAB), and when after this was received the last of stop bits frame, the counter is incremented. Thus, when the SC is a frame at the output of counter 0 at the end of the frame SC (the last of stop bits per frame) the counter is incremented by one and shows that the next byte of data will belong to the first, the channel. After passing the first frame (the last stop bit), the counter is incremented, and so on. Thus, the receiver signal DMX "knows" which channel include current data. If you set any device address, say, 50, and the unit has 6 channels, it just reads the 6 frames, after its internal counter channels to reach 50, and stop reading when it is 55. At that time, sending a new "Reset" (Break) and MAV (which corresponds to the beginning of a new package), the counter is reset to 0. So nothing prevents the console or program to generate a total of 100 bytes of data after the SC for 100 channels and then send a Break. No need to generate all 512 frames (see Figure 1).

What you see on the charts occurs so quickly that the scrolling does not change color. Receivers stores the last received value and respond to the changing values of the change attribute of the device.

The following expression describes the duration of a standard package of DMX512 (1990):

[(88) + (12) + (44) + (CHL * 44) + (CHL * MTBF) + (MTBP)] ISS

where CHL - used by the number of channels,

The ideal duration (in my opinion):

[(120) + (12) + (44) + (CHL * 44) + (0) + (50)] microseconds.

For all 512 channels of the duration of my package will be 22754 microseconds.

Thus, the frequency of regeneration = 1000000 / 22754 = 43.9 Hz.

Refresh may also depend on the performance of the processor used by the algorithm and system architecture.

  Oksid.ch - All about DMX 512

Basic Operations




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