dmx512 communication on the ac led lighting ... · 8 channel display ... sprabr9– january 2013...

Application ReportSPRABR9–January 2013

DMX512 Communication on the AC LED Lighting andCommunications Developer’s Kit

Brett Larimore..................................................................................................................................

ABSTRACT

The AC LED lighting and communications developer’s kit provides a great way to learn and experimentwith using a single MCU to accurately control a series of LED strings and efficiently control the powerstages needed to make the LEDs work. This application report explains how to use theTMDSIACLEDCOMKIT to communicate via DMX512. The accompanying Code Composer Studio™project enables the MCU to control the kit’s power stages, LED strings, and serve as a DMX512 slave.The MCU used to perform all these tasks is a Piccolo™ F28027 microcontroller.

Figure 1. TMDSIACLEDCOMKIT

Code Composer Studio, Piccolo are trademarks of Texas Instruments.All other trademarks are the property of their respective owners.

1SPRABR9–January 2013 DMX512 Communication on the AC LED Lighting and CommunicationsDeveloper’s KitSubmit Documentation Feedback

Copyright © 2013, Texas Instruments Incorporated

http://www.go-dsp.com/forms/techdoc/doc_feedback.htm?litnum=SPRABR9

www.ti.com

WARNINGThis EVM is meant to be operated in a lab environment only and isnot considered by TI to be a finished end-product fit for generalconsumer use.

This EVM must be used only by qualified engineers andtechnicians familiar with risks associated with handling highvoltage electrical and mechanical components, systems andsubsystems.

This equipment operates at voltages and currents that can result inelectrical shock, fire hazard or personal injury if not properlyhandled or applied. Equipment must be used with necessarycaution and appropriate safeguards employed to avoid personalinjury or property damage.

It is your responsibility to confirm that the voltages and isolationrequirements are identified and understood, prior to energizing theboard and or simulation. When energized, the EVM or componentsconnected to the EVM should not be touched.

Contents1 DMX512 Physical Layer and Protocol .................................................................................... 32 Implementation .............................................................................................................. 43 References ................................................................................................................. 11

List of Figures

1 TMDSIACLEDCOMKIT..................................................................................................... 1

2 Example of a DMX512 Master ............................................................................................ 3

3 DMX512 XLR-5 Cable...................................................................................................... 3

4 DMX512 Timing Diagram .................................................................................................. 4

5 DMX512 Interface Schematic ............................................................................................. 5

6 DMX512 Software Timing.................................................................................................. 6

7 Major Files in the DMX512 Project To ................................................................................... 7

8 Channel Display............................................................................................................. 9

9 AC LED Lighting and Communications Board Jumpers and Connectors Diagram............................... 10

List of Tables

1 DMX512 Timing Chart...................................................................................................... 4

2 Worst Case ISR Timings During DMX512 MAB ........................................................................ 6

2 DMX512 Communication on the AC LED Lighting and Communications SPRABR9–January 2013Developer’s Kit Submit Documentation Feedback


http://www.ti.com


www.ti.com DMX512 Physical Layer and Protocol

1 DMX512 Physical Layer and Protocol

1.1 Overview

Digital MultipleX with 512 pieces of information (DMX512) is a common lighting standard that is usedprimarily to control stage lighting, and became the primary method for controlling dimmers and many non-safety critical special effects. Because of its relative simplicity and the stability of the standard, it is alsovery commonly seen in other lighting systems. Depending on network topology and delays, an update rateof approximately 40Hz can be expected per slave. DMX512 is a unidirectional protocol and, because ofthis, employs no error correction.

1.2 Physical Layer

A DMX512 network, known as a DMX universe, consists of one master controlling up to 512 slavedevices. Slaves should be separated into parallel buses that each contain not more than 32 units. Eachbus’s slaves should then be daisy-chained together and each takes their respective information off thebus. The end point of any daisy chain requires a built in 120 Ω terminating resistor. Each receiver shouldnot load the differential line more than 125 pF.

The DMX512 signals are sent via the serial connection standard EIA485 (RS-485).

The standard identifies that XLR-5 connectors be used such that male connectors are receiver ports,whereas, female connectors should be used as transmitting ports. All cables used should be twisted pair.

Common slave devices are dimmers, intelligent lights, or special effect machines.

Figure 2. Example of a DMX512 Master

Figure 3. DMX512 XLR-5 Cable



http://www.ti.com


DATA = 0

Channels

2-256…

MTBP

IDLE BREAK

MAB

(2 bits)

Start Bit

2 Stop

Bits

MTBF

2 Stop

Bits

Start Bit

8 Data

Bits

Start Code Channel 1

Implementation www.ti.com

1.3 Protocol

The DMX512 protocol is characterized as a asynchronous serial data stream that runs at 250 kHz. As aresult, each “bit” will be 4 µs long. DMX512 has one start bit (low), eight bits of data, 2 stop bits and noparity.

Figure 4. DMX512 Timing Diagram

Table 1. DMX512 Timing Chart

Min Typ Max Unit

Break 88 88 1000000 us

Mark After Break (MAB) 8 us

Frame Width 44 us

Start/Data/Stop bits 4 us

Mark Time Between Frames (MTBF) 0 N/A 1000000 us

Mark Time Between Packets (MTBP) 0 N/A 1000000 us

Each packet starts with a break in which the software is held low for at least 88 µs. Following the break,the mark after break (MAB) occurs in which the communications line is held high for two bits. Then, theprotocol cycles through 513 8-bit data frames. The first frame is reserved as the start code in which thedata will be 0. Following the start code frame, a frame is sent that contains the data of channel 1. The nextframe is channel 2 and so on. On the receiver end, this means that a slave receives the data for allchannels, but only needs to react on the channel that corresponds to its address.

2 Implementation

A hardware interface and a Code Composer Studio project were developed to control the LLC resonantstage, control the LED stages, and receive DMX512 commands on a F28027 device. The driver softwarefor DMX512 communications is included with this project and is found largely in the DMX512Comms.c file.

This project can be found at www.ti.com/controlsuite:development_kits\IsoACLighting_vX.X\IsoACLighting-F28027-DMX512

2.1 Hardware Interface

A DMX512 hardware interface has been built into the TMDSIACLEDCOMKIT development kit. SeeFigure 5 for the schematic of this interface. Net terminals DMX-TX and DMX-RX attach to the serialcommunication interface (SCI) peripheral of the F28027 MCU. Note that below TX and RX are relative tothe fixture controlled by the Piccolo F28027.

The host is connected into J8 and then translated into a standard serial signal by a Texas InstrumentsSN65HVD3082ED transceiver.



http://www.ti.com

http://www.ti.com/controlsuite


SN65HVD3082ED

2

2

2

22

5V0

5V0

TP1

TP2

DMX-RX

R3 0R0

R4 DNP

DMX-TX

1

2

3

4

U3

R

nRE

DE

D

8

7

6

5

Vcc

B

A

Gnd

C6

100n

5V0

2

6

1

5

3

4D1BAT54S

R5 10K

J8

1

2

3

4

5

XLR connector(DMX)

Cmn

Data1–

Data1+

NC

NC

www.ti.com Implementation

Figure 5. DMX512 Interface Schematic

2.2 DMX512 Software Driver

The DMX512 software driver relies on the C2000’s SCI peripheral to gather the data and store it in abuffer. This communications peripheral is configurable and can be edited to resemble the DMX512protocol. In the project, the SCI is configured to expect 1 stop bit, no parity, and 8 character bits.

The data rate in the DMX512 protocol pushes the SCI to, for it, a relatively high 512kbaud. In order toeffectively receive the DMX512 signal, the speed of the low speed clock (LOSPCP), which controls theSCI clock speed, was set to 30 MHz and the SCILBAUD bits were set to 14.

The SCI translates the DMX512 data into words with no problem most of the time, however, the BREAKtime specified in the DMX512 protocol does cause some issues. This is because the SCI peripheral doesnot expect the protocol to go high for a significant amount of time and, therefore, sees the BREAK as anerror.

In order to workaround this issue, the software driver switches the pins of the C2000 device betweenGPIO functionality and SCI functionality.



http://www.ti.com


GPIO low-to-high

transitionSCI Error

Change to GPIO Change to SCI and

reset SCI

8us = 480 cycles


Figure 6. DMX512 Software Timing

After a successful transmission, the DMX512 line goes to IDLE for some amount of time with no issue.After this, the DMX512 line enters into the BREAK. Once the SCI has been held low for at least ten bits,the SCI’s break detect (BRKDT) error flag is set and this halts the SCI communication. The automaticsetting of the flag generates a receive interrupt. After determining that the interrupt was caused by anerror, the driver configures the GPIO28 pin to become a GPIO and configures an external GPIO interruptto occur the next time that the GPIO senses a low-to-high transition.

Once the BREAK finishes, the MAB occurs for 2 bits. At the low-to-high transition, the external GPIOinterrupt will fire. Inside this interrupt, GPIO28 is reconfigured to be an SCI pin and the SCI peripheral isreset. By the time the start bit for the Start Code arrives, the SCI is reset and the SCI receives all the newdata.

Because the C2000 CPU may be doing other interrupts, as is the case in the IsoACLighting-F28027-DMX512 project and the way that the DMX512 driver works, the cycle usage of the CPU around the MABis somewhat critical. The MAB is 2 DMX512 bits, which corresponds to 8 µs or 480 F28027 clock cycles.

Therefore, it is assured that the external interrupt and any other high priority interrupts (that may alreadybe running when the external interrupt occurs) can be finished in 480 cycles.

In the IsoACLighting-F28027-DMX512 project, the non-DMX512 ISRs take up a total of 350 cycles. Theexternal interrupt takes about 8 cycles. The ISR-to-entry point delays must also be added in, which for theC2000 device are 14-18 cycles. Table 2 summarizes the worst case cycle usage during the MAB.

Table 2. Worst Case ISR Timings During DMX512 MAB

ISR Plus ISR TriggerISR cycles to Entry Point Delays

Control Loop ISR 230 248

Resonant PWM Update ISR x 3 120 174

GPIO28 L-to-H External Interrupt 8 26

TOTAL 358 448

Spare ISR cycles 122 32

In this chart, the resonant pulse width modulation (PWM) update interrupt is set to happen three times,which is the worst case. The amount of cycles going toward the resonant PWM update depends on theload on the resonant power stage.

Note that even though there are only 32 spare ISR cycles, this is not equivalent to the number of spareCPU cycles. To clarify, there are 32 spare cycles during the MAB until it is possible that occasionally thedriver may miss part of a DMX512 packet and not update during that DMX512 period. Outside of the MABtime there is a significantly larger amount of spare cycles to do host control, and so forth.



http://www.ti.com


IsoACLighting-Main.c file

Initializes the powerstages

Configures the powerstage interrupts

Initializes the DMX512system by calling the

Comms_Init function inIsoACLighting-Comms.c

Runs several periodicallycalled tasks such as

Comms_Run()

IsoACLighting-Comms.c

Serves as a bridging filebetween the Main.c file

and theDMX512Comms.c file

Initializes system variablessuch as the DMX512address that the light

should look at

Starts up the LLCResonant power stage

after some timehas gone by

Calls the DMX512 API

DMX512Comms.c

Initializes DMX512interrupts

Defines the DMX512decoding interruptsand API interface


The DMX512 standard only describes the packet and limitations on the hardware interface. Animplementation of commands is not strictly given, however, often a packet of data relates to an address’sbrightness. For example, a RGB light with addresses 56-58 may set address 56 to be the brightness ofred, address 57 to be the brightness of green and address 58 to be the brightness of blue. The drivergrabs the DMX512 data from all addresses and places it in one large buffer of memory. Once one buffer isfilled, a second buffer is filled and this continues in a ping-pong fashion so that there is always a knowngood buffer. The API function shown below returns a passed address’s most recent data.

Uint16 getValueOfDmxAddress(Uint16 address)

2.3 DMX512 Project

Before working with this project, you should have already run and experimented with the IsoACLighting-F28027 project found at www.ti.com/controlsuite:

development_kits\TMDSIACLEDCOMKIT_v1.0\IsoACLighting-F28027

That project and its documentation thoroughly explain the TMDSIACLEDCOMKIT and how the F28027controls the kit’s power stages. The IsoACLighting-F28027-DMX512 project builds on the knowledgefound there.

Hardware-wise, the only change that needs to be done to make the DMX512 project work is that thejumpers at [Main]-J6 and [Main]-J7 both need to be moved and placed to connect positions 2 and 3.

The key software difference between the IsoACLighting-F28027 project and the IsoACLighting-F28027-DMX512 project is that the IsoACLighting-Comms.c file has changed and now interfaces and callsfunctions in the DMX512Comms.c file. The Comms.c file also initializes and turns on the resonant stageso that the DMX512 interface can directly change the brightness of the LED strings without needing to doanything with the LLC resonant stage. This DMX512Comms.c file contains the DMX512 driver and the APIinto the driver. Figure 7 gives some details on the major files used in the DMX512 project.

Figure 7. Major Files in the DMX512 Project To



http://www.ti.com




To run the project and have DMX512 communications work, you need a DMX512 master such as theEnttec USB Pro. For a computer to interface with this master, you require some software such as LightFactory (http://www.lifact.com/). You also need a DMX compatible cable such as Newark part number18J1683.

1. Run the software and configure the hardware as instructed in build 1 and 2 of theTMDSIACLEDCOMKIT-CCS guide.

2. Attach the USB cable to [M8]-JP1.

3. Ensure that [Main]-J3 is populated.

4. Put jumpers across positions 2 and 3 of [Main]-J6 and [Main]-J7.

5. Attach a DMX512 cable to [Main]-J8.

6. Setup the DMX512 master and software as instructed in the master’s user manuals and guides.

7. Connect a 12 V DC supply to [M7]-JP1.

8. Switch [M7]-SW1 to the “Ext” position.

9. Open Code Composer Studio.

10. Import the IsoACLighting-F28027-DMX512 project found at www.ti.com/controlsuite:

development_kits\TMDSIACLEDCOMKIT_vX.X\ IsoACLighting-F28027-DMX512

11. Compile the software.

12. Connect and flash the code by clicking the “bug” button.

13. Reset the processor and then click restart (so that the program starts at the beginning of main) inCode Composer Studio.

14. Enable real-time mode and enable continuous refresh of the watch window in Code Composer Studio.

15. Click the green play button to run the software. (Step 16 should be done shortly after this step iscomplete.)

16. Carefully plug the AC cable into the wall. Once this step is complete, the board will be dangerous totouch.

Note that the LLC resonant power supply is automatically set to turn on about 10 seconds after theboard is powered.

17. Use the DMX512 software to communicate brightness information to the kit. By default the DMXaddress each LED string is looking at is address 31-36. The DMX512 commands to these address willimpact Gui_Iled[0-5] and the current reference given to each LED string.

18. Look at rdata[dmxBufferNum_LastGood] to see the last good buffer of all 512 pieces of DMX512 datain Code Composer Studio.

19. Set each applicable DMX512 address to 0 when done.

20. Unplug the power cable from the wall.

21. Wait at least 60 seconds before touching the board.

NOTE: This demo can also be run without the external DC/DC power supply connected and withoutCode Composer Studio. However, it is safer to use the external power supply first. Once theDMX512 code is flashed into the device (which is done in the procedure above), you canrerun the above with the following exceptions: remove the DC/DC supply, switch [M7]-SW1away from “Ext”, and skip steps 10 - 12 and 16.



http://www.ti.com

http://www.lifact.com/




Figure 8. Channel Display



http://www.ti.com


[Main

]J2

–4

00

V-t

o-1

2V

en

ab

leju

mp

er

[Main

]B

S3

–B

an

an

aJa

ck

for

Re

so

na

nt

Inp

ut

[Main

]J20

–4

00

V-t

o-1

8V

en

ab

leju

mp

er

[M8]

JP

1–

US

BC

on

ne

ctio

nfo

ronboa

rde

mu

latio

n

[Main

]T

B1-T

B6

–L

ED

str

ing

co

nn

ecto

rsfo

rL

ED

pa

ne

l

[Main

]B

S1

–B

an

an

aJa

ck

for

PF

Co

utp

ut

[Main

]B

S2

–B

an

an

aJa

ck

for

prim

ary

sid

eG

ND

[Main

]J1

–1

00

-pin

DIM

Mco

ntr

olC

AR

Dco

nn

ecto

r

[M7

]S

W1

–L

ow

Vo

lta

ge

Po

we

rS

witch

[Main

]B

S5

Ba

na

na

Ja

ck

for

secondary

sid

eG

ND

[Main

]B

S4

Ba

na

na

Ja

ck

for

Re

so

na

nt o

utp

ut

[Main

]B

S6

–B

an

an

aJa

ck

for

LE

DB

us

inp

ut

[M7]

JP

1–

12

-15

Ve

xte

rna

lp

ow

er

co

nn

ecto

r

[Main

]T

B7

–D

ALI

co

mm

un

ica

tio

ns

he

ad

er

[Main

]J8

–D

MX

51

2co

mm

un

ica

tio

ns

co

nn

ecto

r

[Main

]J4-J

7–

Co

mm

un

ica

tio

ns

se

lectio

nju

mpers

[Ma

in]

P1

–U

niv

ers

al A

CC

onnecto

r(8

5-2

50

Va

c)

[Main

]J3

–JTA

GT

RS

Tn

Ju

mp

er

[Main

]J16

+1

2V

DC

header

for

fan


Figure 9. AC LED Lighting and Communications Board Jumpers and Connectors Diagram



http://www.ti.com


www.ti.com References

3 References• www.ti.com/controlsuite:

– TMDSIACLEDCOMKIT_CCS — provides detailed information on the IsoACLighting project withinCode Composer Studio. The document goes through the project in an easy to use labstyle format.

development_kits\TMDSIACLEDCOMKIT_vX.X\~Docs\ TMDSIACLEDCOMKIT_CCS.pdf

– TMDSIACLEDCOMKIT-HWdevPkg — a folder containing various files related to the hardware onthe AC LED Lighting and Communications Developer’s Kit board (schematics, bill of materials,Gerber files, PCB layout, and so forth).

development_kits\TMDSIACLEDCOMKIT_vX.X \ ~TMDSIACLEDCOMKIT-HwdevPkg[R4]\

– TMDSIACLEDCOMKIT-HWGuide — presents full documentation on the hardware found on the ACLED Lighting and Communications Developer’s board.

development_kits\TMDSIACLEDCOMKIT_vX.X\~Docs\ TMDSIACLEDCOMKIT -HWGuide.pdf

• DMX512 Standard – Gives links to the DMX512 and DMX512-A standard created by USITT andmaintained by ESTA. http://www.usitt.org/Resources/Standards2/DMX512

• OpenDMX.net – Presents some useful information on DMX512.

– DMX512-A wiki page: http://www.opendmx.net/index.php/DMX512-A

– OpenDMX.net wiki page: http://www.opendmx.net/index.php/OpenDMX.net

• Ujjal’s DMX512 Pages – provides a good overview of DMX512, implementation and history.

– What is DMX512? http://www.dmx512-online.com/whats.html



http://www.ti.com


http://www.usitt.org/Resources/Standards2/DMX512

http://www.opendmx.net/index.php/DMX512-A

http://www.opendmx.net/index.php/OpenDMX.net

http://www.dmx512-online.com/whats.html


IMPORTANT NOTICE

Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and otherchanges to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latestissue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current andcomplete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of salesupplied at the time of order acknowledgment.

TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s termsand conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessaryto support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarilyperformed.

TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products andapplications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provideadequate design and operating safeguards.

TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, orother intellectual property right relating to any combination, machine, or process in which TI components or services are used. Informationpublished by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty orendorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of thethird party, or a license from TI under the patents or other intellectual property of TI.

Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alterationand is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altereddocumentation. Information of third parties may be subject to additional restrictions.

Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or servicevoids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.TI is not responsible or liable for any such statements.

Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirementsconcerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or supportthat may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards whichanticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might causeharm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the useof any TI components in safety-critical applications.

In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is tohelp enable customers to design and create their own end-product solutions that meet applicable functional safety standards andrequirements. Nonetheless, such components are subject to these terms.

No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the partieshave executed a special agreement specifically governing such use.

Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use inmilitary/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI componentswhich have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal andregulatory requirements in connection with such use.

TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use ofnon-designated products, TI will not be responsible for any failure to meet ISO/TS16949.

Products Applications

Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive

Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications

Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers

DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps

DSP dsp.ti.com Energy and Lighting www.ti.com/energy

Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial

Interface interface.ti.com Medical www.ti.com/medical

Logic logic.ti.com Security www.ti.com/security

Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense

Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video

RFID www.ti-rfid.com

OMAP Applications Processors www.ti.com/omap TI E2E Community e2e.ti.com

Wireless Connectivity www.ti.com/wirelessconnectivity

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265Copyright © 2013, Texas Instruments Incorporated

http://www.ti.com/audio

http://www.ti.com/automotive

http://amplifier.ti.com

http://www.ti.com/communications

http://dataconverter.ti.com

http://www.ti.com/computers

http://www.dlp.com

http://www.ti.com/consumer-apps

http://dsp.ti.com

http://www.ti.com/energy

http://www.ti.com/clocks

http://www.ti.com/industrial

http://interface.ti.com

http://www.ti.com/medical

http://logic.ti.com

http://www.ti.com/security

http://power.ti.com

http://www.ti.com/space-avionics-defense

http://microcontroller.ti.com

http://www.ti.com/video

http://www.ti-rfid.com

http://www.ti.com/omap

http://e2e.ti.com

http://www.ti.com/wirelessconnectivity

dmx512 communication on the ac led lighting ... · 8 channel display ... sprabr9– january 2013...

Documents