DMX has a number of timing variables. The information presented here will probably be useful for only a small proportion of users, but can assist in getting troublesome DMX equipment to work. If you need further information, the book "Recommended Practice for DMX512 - A guide for installers and users" is highly recommended, and available from PLASA or ESTA.
There are several areas where DMX timing can vary in a DMX packet. Each packet follows the format shown above.
First, a break occurs telling the receiver that this is the start of a new packet. Then the line is driven high for the Mark after Break (MAB) time. Then follows the start code, followed by the "post start" time. Then there follows the channel data, during which the line can be high (idle) for a variable amount of time between channels, known as the interbyte time. Finally after the last channel the line goes high(idle) for the interpacket delay time until the break of the next packet.
The following are the minimum values allowable by the ESTA DMX-512A standard :
| Timing Parameter |
Minimum |
Maximum |
| Break |
92μs |
Note 1 |
| Mark-After-Break |
12μs |
Note 1 |
| Post-Start |
8μs (Two stop bits) |
Note 1 |
| Interbyte |
8μs (Two stop bits)
|
Note 1 |
| Interpacket |
8μs (Two stop bits)
|
Note 1
|
Note 1 : These timings can be any value to add up to make a packet length of up to one second.
As you can see a very wide variety of timings is permissible. For reference, here are the timings for some different ETC products.
Ion, Element, Congo, Congo jr and Congo Kid Consoles
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Maximum
|
36
|
142
|
128
|
24
|
12
|
12
|
|
Fast
|
36
|
142
|
128
|
27
|
18
|
16
|
|
Medium
|
36
|
142
|
128
|
34
|
30
|
30
|
|
Slow
|
36
|
142
|
128
|
42
|
46
|
44
|
4 Port Gateway, Software version 4.0.5.9.0.36, Net2 Mode
Observations
- Variable
DMX output speed is not implemented
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Any
|
8
|
126-132
|
56
|
24
|
8
|
784-1260
|
2 Port Gateway, Software version 4.0.5.9.0.36, Net2 Mode
Observations
- Variable
DMX output speed is not implemented
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Any
|
8
|
176
|
12
|
23
|
8
|
1260
|
2 Port Gateway, Software version 1.0.0.9.0.83, ACN Mode
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Maximum
|
8
|
176
|
12
|
22
|
8
|
176
|
|
Fast
|
8
|
176
|
12
|
24
|
8
|
2160
|
|
Medium
|
12
|
240
|
60
|
29
|
12
|
4200
|
|
Slow
|
13
|
288
|
60
|
33
|
12
|
8240
|
2 Port Node, Software version 4.1.3.9.0.6
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Maximum
|
8
|
88-93
|
48
|
22
|
8
|
8
|
|
Fast
|
12
|
156
|
48
|
25
|
12
|
90
|
|
Medium
|
16
|
184
|
74
|
27
|
16
|
162
|
|
Slow
|
24
|
226
|
100
|
31
|
24
|
254
|
Smartfade, Software version 3.0.0
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Maximum
|
0
|
176
|
16
|
22
|
0
|
0
|
|
Fast
|
12
|
176
|
44
|
27 |
4
|
2000
|
|
Medium
|
16
|
220
|
100
|
34 |
16
|
4000
|
|
Slow
|
36
|
264
|
100
|
50 |
36
|
8000
|
Express, Software version 3.1
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Maximum
|
32
|
94
|
26
|
26
|
12
|
1160
|
|
Fast
|
32
|
138
|
28
|
26
|
12
|
1160
|
|
Medium
|
32
|
184
|
32
|
26
|
12
|
2120
|
|
Slow
|
32
|
270
|
50
|
31
|
12
|
6960
|
Four port node, Software version 4.1
|
|
Post Start (μs)
|
Break (μs)
|
MAB (μs)
|
Packet (ms)
|
Interbyte (μs)
|
Interpacket Idle (μs)
|
|
Maximum
|
8
|
94
|
8
|
23
|
8
|
1140
|
|
Fast
|
8
|
142
|
13
|
26
|
8
|
3040
|
|
Medium
|
8
|
188
|
18
|
27
|
8
|
5160
|
|
Slow
|
8
|
282
|
33-35
|
32
|
8
|
8800
|