Wow! Lot's of questions and answers in this thread. No doubt I will not get all of them so let me know if there is more you'd like to know.
D192: Yes, it was named for the rack's ability to have 192 dimmers
in one chassis. The D192, or
Colortran protocol, was packetized very similar to
DMX with the primary difference being that the baud rate was 153.6k as opposed to 250k for
DMX. There was support for 512 dimmers in the
protocol. The change to control modules [which I highly recommend be done at Lite-Trol] is an oscillator and a
resistor responsible for the required new packet timeout for the faster baud rate. Remember that the controller in the installation rack is a state machine and is highly reliant on oscillators and analog components to properly operate.
DMX: Yes, five places exist where timing can be modified: Interpacket, Interbyte, Post Start, Break and
Mark After Break. This would be one of two reasons why
DMX is not always
DMX. Add in to this differences in hardware implementations and grounding schemes over the years and it's a little surprising most stuff in fact works together at all. Eventhough the new standards tighten up acceptable hardware implementations, and all versions of the standard place the burden of accepting odd timings on the recieving device, we all know these devices have gotten cheaper and hence sometimes porrly designed. The common solution is to now burden the transmitter [console] with solving timings mismatches.
Express consoles: Indeed
DMX refresh rate got a little slower as we went from v2.0 code to the v3.x series. Changing speeds between Max/Fast/
Med/Slow really only added some timing in between packets [Interpacket] and added time to Break and MAB, but Interbyte time was always close to zero [or 8usec depending on your terminology]. Unfortunately most cheap
DMX receivers need extra Interbyte time, although not likely the case in a
Colortran pack/rack. To be honest, I've never verified what
DMX timings change when an
Express has its number of outputs changed. Larry [one of the sw engineers] had told me a long time ago that it only sets some limitations in patch and displays without affecting anything in timing. I do know that no mater the settings, both output ports always
send 513 bytes [counting the Start Code].
Idea: Not sure what the timing difference is between 256/512 outputs. Based on the very slow/small
processor in the
console, it is highly likely that changing the number of outputs affects not only output speed but overall
console operating speed. This is indeed why the
switch was installed - that is, to get the
console to run faster set at 256, not to speed match to receivers. I do not remember the data rates. No doubt this change is just enough to get the
Colortran dimmers to receive the
DMX. My guess would be an increase in both Interpacket and Interbyte time got them to sync up.
Does that
cover enough? Let me know,
David