Subject: Re: DMX Standard req.

From: [email-masked] (John Paul Flowers)
Date: 10 May 1995 17:49:52 GMT

David Lomas (davidl@p9news) wrote:
: Could anyone please send me or point me in the direction of some documentation 
: about the DMX control system. I need information ranging from voltage levels & 
: comms protocol to the actual format of messages.

USITT.
10 west 19th street, suite 5A
NY NY,
10011-4206

212-924-9088
FAX 924-9343

Publishes DMX-512 and it should cost something like $25.

OK,

I found my copy of the DMX-512 standard, here are some interesting facts.

5.0 DATA PROTOCOL

Data transitted shall be in asynchronous serial format. Dimmer level data
shall be transmitted sequentially, beginning with dimmer 1 and ending with the 
last implemented dimmer, up to a maximum of 512. Prior to the first level
transmitted, a RESET signal shall be transmitted followed by the NULL START
code. Valid dimmer levels shall be 0 to 255 decimal (00 to FF Hex)
representing dimmer control input levels of OFF to FULL in a linear relation-
ship. These numeric values shall not necessarily have any relationship to the 
actual dimmer output, which shall be determined within the dimmer itself.

5.0.1 RESET SIGNAL

The RESET signal shall consist of a BREAK lasting at least 88 usec (two frame
times). A BREAK shall be defined as a high-to-low transition followed by a 
low of at least 88 usec.  A BREAK f any duration exceeding 88 usec shall be
allowed. Multiple RESETS with no level information between shall be allowed.

5.0.2 NULL START CODE

The NULL START code shall be defined as a properly framed NULL character (all
zeros) following a RESET. The NULL START code is the data packet indentifier
which indentifies subsequent data as sequential dimmer level information.

6.0 DATA FORMAT
 
The data transmission format for each level transmited shall be as follows:

BIT POSITION		DESCRIPTION
     1                  Start Bit, Low or SPACE
 2 through 9		Dimmer level Data Bits, Least Significant Bit
			to Most Significant Bit Positive logic
   10, 11		Stop Bits, High or MARK
   Parity		Not Transmitted

7.0 DATA RATE

The data rate and associated timing shall be as follows:
Data Rate:		250 Kilobits per second
Bit Time:		4.0 microseconds
Frame Time:		44.0 microseconds
Maximum Update:		22.71 milliseconds
Rate for 512 dimmers	44.03 times per second
including RESET and START

7.1 Timing Diagram.

johnf> Sorry I can't send this to you well in ASCII, I can
scan it and make a GIF or jpg of it and uuencode if you need it.

-- 
**************************************************************************** 
*   John P. Flowers                   _\|/_______________________          *
*   [email-masked]                   /|\ We can tell how                 *
*   HP Santa Clara Division                far gone you are!               * 
*   Precision Motion Control R&D                                           *
****************************************************************************

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From: [email-masked] (Albert Buralli)
Date: 10 May 1995 18:47:24 GMT

The complete DMX512 standard can be obtained from the USITT in New York.
Sorry , I don't have the number with me.  If you don't have any luck post 
a return message with any specific questions and I'll be happy to look it 
up for you.

                                                               Lee 
Buralli
                                                               Lakeside 
Lighting
                                                               Orangevale,
Ca.

---

From: davidl@p9news (David Lomas)
Date: 10 May 1995 14:12:52 BST

Could anyone please send me or point me in the direction of some documentation 
about the DMX control system. I need information ranging from voltage levels & 
comms protocol to the actual format of messages.

Cheers in advance,

Dave Lomas