The_Terg said:
The problem with serial is that I think it's a Liiiitle too slow for use for
DMX.
This much is true. The fastest PC serial port runs at less than half the bit-rate of DMX-512.
If you think about it,
DMX is nearly identical to
MIDI in the way that it uses individual commands (
channel 53 off,
channel 53
intensity 127....
etc) sent at a rapid speed to achieve control.
This is not true. Every DMX-512 packet contains information for all channels, regardless of whether there are any changes. The
DMX packet starts with a BREAK (data held low) of at least 88 microseconds, a
MARK (data held high) of at least 8 microseconds, one byte to indicate packet type (usually zero, to indicate
dimmer control), then one byte of control information for each
channel. The
channel address is implied by the byte's position in the packet. The first byte after the packet type is
channel 1, the second is
channel 2 and so on. A packet telling
channel 53 to go to
intensity 127 will include commands for all the other channels as well, even if there is no change on any of those other channels.
MIDI does work the way you said; each packet consists of a status byte (note ON, for example), a note number (range 0-127) and a velocity (also in the range 0-127). There are exceptions, but that's the basic scheme.
By the way, the maximum bit-rate for most PC serial ports is 115,200 bps.
MIDI is locked solid at 31,250 bps, but the hardware is a current-loop
topology, incompatible with RS-232. DMX-512 hardware is RS-485, for which there are inexpensive serial-port converters, but it requires a bit-rate of 250,000 bps, beyond the range of most PC serial ports.
John