> On 2/24/06, G=F6khan SEVER <gstr2005@gmail.com> wrote:
>> after working a bit with those little ligthy things, i'm planning to
>> implement lighting control system based on dmx512
>> protocol. Because of i'm newbie to this subject i need some introductory
>> opinions about how the system work generally.
>> After grasping general working of the controll system i will strive on
>> techinal details such as how the dmx512 protocol
>> works?, how can the each unit adressed, what must be the proper
>> hardware-software design for this system and of course a
>> windows based controller gui considerations...
>
> Check out http://www.dmx512-online.com. It's a good technical overview
> for non technical people. As always, nothing beats owning the actual
> spec (I do). It's about $30 from ESTA.
>
> Josh


And the basic DMX512 protocol is pretty straightforward. It's EIA485, send
a break, send a mark after break, send a start byte (zero for control of
dimmers), send a byte for dimmer 1, send a byte for dimmer 2, repeat as
necessary. You generally have to send at least 24 dimmer values, up to a
maximum of 512. Data is 8 data bits, no parity, two stop bits at 250kbps.
The tricky part on a pic is synchronizing the break with the data (the
break command in some newer pics is not long enough, I do generate the
break using another PIC pin). To get around the synchronization problem, I
use a timer interrupt instead of a uart interrupt. Then, when I put a byte
in the uart transmit register, I know that byte starts transmission right
now. Otherwise, you have to try to figure out how long it'll be in the
holding register, then the shift register, etc. Using a timer interrupt
makes it pretty simple. From there out, it's a state machine.

Good luck!

Harold


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