Talk:DMX512-A - Revision history

90.185.54.180: clean-up

2009-12-09T21:26:43Z

clean-up

90.185.54.180: more cleaning, termination tolerance

2009-12-09T16:43:07Z

more cleaning, termination tolerance

90.185.54.180: removed obsolete text, it is already mentioned elsewhere

2009-12-09T16:28:41Z

removed obsolete text, it is already mentioned elsewhere

90.185.54.180: Added and corrected some more details.

2009-12-09T16:25:43Z

Added and corrected some more details.

Nomis52: Talk:DMX moved to Talk:DMX512-A

2009-07-12T00:43:08Z

Talk:DMX moved to Talk:DMX512-A

Beier: Added timing table, extra voltage note

2009-06-10T16:21:49Z

Added timing table, extra voltage note

90.185.54.180: /* More suggestions and info */

2009-03-31T20:33:10Z

‎More suggestions and info

Beier: New section: More suggestions and info

2008-08-15T17:24:55Z

New section: More suggestions and info

Beier: New page: == Timings == The clock rate is 250 kHz so each symbol bit on the wire is 4 microseconds long (period time). Frame rate is ?? Packet rate is typically around 44 Hz when all frames are sen...

2008-07-18T15:40:14Z

New page: == Timings == The clock rate is 250 kHz so each symbol bit on the wire is 4 microseconds long (period time). Frame rate is ?? Packet rate is typically around 44 Hz when all frames are sen...

New page

== Timings ==
The clock rate is 250 kHz so each symbol bit on the wire is 4 microseconds long (period time).

Frame rate is ??
Packet rate is typically around 44 Hz when all frames are sent.

== RDM protocol additions ==
The name of the standard is: ANSI/ESTA 1.20, Entertainment Technology - Remote Device Management over USITT DMX512
???
Mark (beginning of frames)
Mark After Break (beginning of frames)

Mark time between packet
Mark time between frames

== Use of category 5 UTP or STP ==
New cable types is used, and may be officially accepted.
http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_08

The use of modular plugs like 8P8C (RJ45) or 6P4C (RJ11)

The cabling for DMX512-A should be described in the document called "BSR E1.27-1 -- Portable Control Cables for Use with USITT DMX512/1990 and E1.11 [DMX512-A]"

== Sender/receiver topologiess ==
To avoid ground loops and improve reception performance, transmitters and/or receivers can be grounded/floating/non-isolated ???
http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_15
There are different topologies, and not all will work together. There are no requirement for what topology to use in the DMX specification from 1990, so it was added to DMX512-A.

Transmitters should use "earth ground" as a reference for the positive/negative voltages that is put on the two data lines. If they don't, it must be clearly marked on the product and in the manual.
Receivers should be ...?

@@ Line 1: / Line 1: @@
+== connectors ==
-Symbol length is 4 +/- 0.08us for 245 - 255 k baud/s, with non-return-zero between symbol bits. To transmit 8 data bits it take 11 symbols because the use of one start bit and two stop bits around each data byte. Slot/address number is known by counting slots from the long packet break in the beginning of each packet.
+The use of modular plugs like 8-position modular connector (8P8C or RJ45) or 6P4C (RJ11)? Is there any allowance for other than 8 position modular connectors?
+Some product (cheap dimmers) have 6 position connectors (RJ11).
 == Sender/receiver topologies ==
@@ Line 82: / Line 12: @@
 Receivers should be ...?
 == Voltages ==
 At http://www.dmx512-online.com/physl.html there is an example wit D1+ at +5V and D1- at -5V, and considering [http://focus.ti.com/lit/an/slla070c/slla070c.pdf page 12 in this document from TI] it is presumably a wrong interpretation.
@@ Line 99: / Line 19: @@
 [http://www.dmx512-online.com/physl.html This web page] cites RS485 as having a upper limit of +12/-7 V with respect to ground. This probably refers to common mode loading voltages that receivers must work with. I.e. one of the data wires is allowed to reach +12 or -7 V but the opposite wire must not be at the other extreme, but only differ by 6 V maximum.
 == Debugging tips ==

@@ Line 2: / Line 2: @@
 The clock rate is 250 kHz so each symbol bit on the wire is 4 microseconds long (period time).
 Symbol length is 4 +/- 0.08us for 245 - 255 k baud/s, with non-return-zero between symbol bits. To transmit 8 data bits it take 11 symbols because the use of one start bit and two stop bits around each data byte. Slot/address number is known by counting slots from the long packet break in the beginning of each packet.
@@ Line 44: / Line 40: @@
 New cable types is used, and may be officially accepted.
 http://www.usitt.org/DMX512FAQ.aspx#a9
-  (old link is http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_08)
+  (old link is [http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_08])
@@ Line 109: / Line 105: @@
-a but the spec says that the differential maximum from transmitters is 6 V, according to
+Termination resistor tolerance is 120 Ohm +5 % / -10 % (108 – 126 Ohm).
 == Debugging tips ==

@@ Line 5: / Line 5: @@
 Packet rate is typically around 44 Hz when all frames are sent.
-== RDM protocol additions ==
+== DMX Timing table ==
 Symbol length is 4 +/- 0.08us for 245 - 255 k baud/s, with non-return-zero between symbol bits. To transmit 8 data bits it take 11 symbols because the use of one start bit and two stop bits around each data byte. Slot/address number is known by counting slots from the long packet break in the beginning of each packet.

@@ Line 16: / Line 16: @@
 DMX Timing table
-Symbol length is 4 +/- 0.08us for 245 - 255 k baud/s, with non-return-zero between symbol bits. To transmit 8 data bits it take 11 symbols because the use of one start bit and two stop bits around each data byte.
+Symbol length is 4 +/- 0.08us for 245 - 255 k baud/s, with non-return-zero between symbol bits. To transmit 8 data bits it take 11 symbols because the use of one start bit and two stop bits around each data byte. Slot/address number is known by counting slots from the long packet break in the beginning of each packet.
 {|border=1
 ||'''Name'''		|| '''Tx requirement'''	|| '''Typical/suggested Tx'''	|| '''Rx requirement'''
 |-
-||Break <br> (the packet start)	|| >= 92 us || 100-120 us (Ujjal) <br> 176 us (DMX512-A-2004)|| >= 88 us
+||Break (a space)<br> (the packet start)	|| >= 92 us || 100-120 us (Ujjal) <br> 176 us (DMX512-A-2004)|| >= 88 us
 |-
-||Mark after break <br> (in packet start)	|| >= 8 us || 12 us (Ujjal)	|| 4 us - < 1 s backward compatible <br>8 us - < 1 s DMX512-A-2004
+||Mark after break <br> (in packet start)	|| >= 8 us || 12 us (Ujjal)	|| 4 us  – < 1 s backward compatible <br>8 us  – < 1 s DMX512-A-2004
 |-
 ||Slot/frame width	|| 44 us		|| 44 us			|| 44 us
 |-
-||Inter-slot/frame time	|| < 1 s		|| minimal			|| < 1 s ?
+||Inter-slot/frame time	<br>Mark time between slots|| < 1 s	|| minimal	|| < 1 s
 |-
-||Mark before break <br> (Idle time after packet)|| < 1 s || 0 - 1 s  ?		|| < 1 s ?
+||Mark before break <br> (Idle time after packet)|| < 1 s 	|| minimal	|| < 1 s
 |-
-||Break to Break time, also<br>(DMX2512 packet length) || 1204 us -1 s		||				|| 1196 us - 1.25 s
+||Break to Break time <br>(DMX2512 packet length) || 1204 us  – 1 s|| minimal|| 1196 us  – 1.25 s
 |}
 The slot time must be precise, or else the receiver should discard the whole packet, e.g. if the second stop bit is missing.
 There must be at least one packet with start code=0 per second, and a receiving product must specify what happens when this time is exceeded.
-Ervin Rol has shown the timing values from the DMX standard.
+Here is a nice overview of the different parts of a DMX packet with timings etc.: http://www.erwinrol.com/index.php?stagecraft/dmx.php.
 == Use of category 5 UTP or STP ==
 New cable types is used, and may be officially accepted.
-http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_08
+http://www.usitt.org/DMX512FAQ.aspx#a9
 The cabling for DMX512-A should be described in the document  called "BSR E1.27-1 -- Portable Control Cables for Use with USITT DMX512/1990 and E1.11 [DMX512-A]"
-== Sender/receiver topologiess ==
+A PDF shows the research and measurements that shows cat. 5 cable is good enough for DMX.
 To avoid ground loops and improve reception performance, transmitters and/or receivers can be grounded/floating/non-isolated ???
 http://www.usitt.org/standards/DMX512_FAQ.html#FAQ_15
@@ Line 76: / Line 112: @@
 [http://www.dmx512-online.com/physl.html This web page] cites RS485 as having a upper limit of +12/-7 V with respect to ground. This probably refers to common mode loading voltages that receivers must work with. I.e. one of the data wires is allowed to reach +12 or -7 V but the opposite wire must not be at the other extreme, but only differ by 6 V maximum.
-Transciever chips made for 5 V:
+Transceiver chips made for 5 V:
 Linear Technology LTC485: http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1007,C1017,P2064
 National semiconductor LMS485: http://www.national.com/mpf/LM/LMS485.html

@@ Line 13: / Line 13: @@
 Mark time between packet
 Mark time between frames
@@ Line 44: / Line 72: @@
 This give the maximum power dissipation is P= U*U/R= 6*6/120 = 300 mW. So it is best to use 1/2 W resistors.
-This web page cites RS485 as having a upper limit of +12/-7 V with respect to ground: http://www.dmx512-online.com/physl.html
+At http://www.dmx512-online.com/physl.html there is an example wit D1+ at +5V and D1- at -5V, and considering [http://focus.ti.com/lit/an/slla070c/slla070c.pdf page 12 in this document from TI] it is presumably a wrong interpretation.
 Transciever chips made for 5 V:
@@ Line 50: / Line 80: @@
 National semiconductor LMS485: http://www.national.com/mpf/LM/LMS485.html
 National semiconductor DS75176B (used in Martin PAL 1200, Lite-Puter DX-625 and a cheap Eurolite DMX console) http://www.national.com/mpf/DS/DS75176B.html
 == Debugging tips ==
@@ Line 56: / Line 89: @@
 How can reverse polarity be detected?

← Older revision	Revision as of 00:43, 12 July 2009
(No difference)

← Older revision		Revision as of 20:33, 31 March 2009
Line 32:		Line 32:

	== More suggestions and info ==		== More suggestions and info ==
		+
		+	Here is also a nice overview of the different parts of a DMX packet with timings etc.:
		+	http://www.erwinrol.com/index.php?stagecraft/dmx.php

	== Voltages ==		== Voltages ==

← Older revision		Revision as of 17:24, 15 August 2008
Line 30:		Line 30:
	Transmitters should use "earth ground" as a reference for the positive/negative voltages that is put on the two data lines. If they don't, it must be clearly marked on the product and in the manual.		Transmitters should use "earth ground" as a reference for the positive/negative voltages that is put on the two data lines. If they don't, it must be clearly marked on the product and in the manual.
	Receivers should be ...?		Receivers should be ...?
		+
		+	== More suggestions and info ==
		+
		+	== Voltages ==
		+
		+	The power dissipation in the 120 Ohm terminating resistors depends on the differential voltage between the two data wires.
		+	If the transmitter only makes a 5 V differential voltage, the power dissipation is P= UU/R= 55/120 = 208 mW.
		+
		+	According to http://focus.ti.com/lit/an/slla070c/slla070c.pdf the maximum absolute differential voltage allowed by the EIA485 standard is 6 V.
		+	This give the maximum power dissipation is P= UU/R= 66/120 = 300 mW. So it is best to use 1/2 W resistors.
		+
		+	This web page cites RS485 as having a upper limit of +12/-7 V with respect to ground: http://www.dmx512-online.com/physl.html
		+
		+	Transciever chips made for 5 V:
		+	Linear Technology LTC485: http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1007,C1017,P2064
		+	National semiconductor LMS485: http://www.national.com/mpf/LM/LMS485.html
		+	National semiconductor DS75176B (used in Martin PAL 1200, Lite-Puter DX-625 and a cheap Eurolite DMX console) http://www.national.com/mpf/DS/DS75176B.html
		+
		+	== Debugging tips ==
		+
		+	Links to simple testers?
		+
		+	How can reverse polarity be detected?