DMX512 Receiving Device with XC836 - description

XC82x/XC83x
DMX512 Receiving Device with
XC836
AP08131
Application Note
V1.1, 2012-10
Microcontrollers
Edition 2012-10
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2012 Infineon Technologies AG
All Rights Reserved.
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DMX512 Receiving Device with XC836
AP08131
XC82x/XC83x
Revision History: V1.1 2012-10
Previous Version(s):
Page
Subjects (major changes since last revision)
26
Figure 26. R5 changed from 1k to 560R
28
Figure 28. Updated schematic version number from 1.4 to 1.5
-
Updated all Figures with DALI-DMX512 Board version 1.5
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Application Note
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Table of Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
2.1
2.2
2.2.1
2.2.2
2.3
Overview of DMX512 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Physical Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
XLR-5 Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Isolated Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DMX512 Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
3.1
3.1.1
3.1.2
3.1.3
3.2
3.2.1
3.2.2
3.2.3
3.2.4
DMX512 Implementation with XC836 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
DMX512 Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
DIP Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Power Supply Connector and SPD Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Software Abstraction Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Interrupt Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
List of Source Code Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Recommended DMX512 Signal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4
4.1
4.2
4.3
DMX512 Software Stack Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Configuring the Required DMX512 Slots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alternative Pinouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DMX512 Address Setting by Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
15
15
16
5
5.1
5.2
5.3
5.4
5.5
5.6
Evaluating DALI - DMX512 Board for LED Color Control Application . . . . . . . . . . . . . . . . . . . . .
Connecting the Boards in a Daisy-Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting the DMX512 Address with DIP switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting the Transmitting Device to the Daisy Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Powering Up the Receiving Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Powering Up the Transmitting Device from USB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Controlling LED Color with the Transmitting Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
17
17
18
18
19
19
6
6.1
6.2
6.3
Enhancement Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Packet Length Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Valid Address Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Packet Loss Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
22
23
24
7
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5
5
6
6
7
7
Appendix - DALI-DMX512 Board Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Appendix - DMX512 Software Stack Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Appendix - Suggested Circuit to Fulfill Isolated Topology Requirement . . . . . . . . . . . . . . . . . . 31
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Introduction
1
Introduction
DMX512 is a communication protocol commonly used in stage lighting applications. It describes the digital data
transmission between the controller and the stage equipment, such as a washlight, moving head, or fog machine
for example. The E1.11-2008 USITT DMX512-A protocol is maintained by ESTA (Entertainment Service and
Technology Association).
This application note describes the implementation of a DMX512 software stack to act as a receiving device, using
the XC836 microcontroller from Infineon. We start with an overview of the DMX512, where the system architecture
and protocol structure are explained, then discuss the implementation using the XC836 microcontroller, and finally
describe the integrated DALI-DMX512 board which can be used to control the on-board RGB LED via the DMX512
protocol.
2
Overview of DMX512
DMX512 is a packet-based, asynchronous, serial and unidirectional communication protocol. Because there is no
error checking or correction mechanism specified in the standard, this makes it relatively simple, but also means
that it is unsuitable for safety-critical applications.
DMX512 uses differential signals for communication specified by the RS-485 standard. Therefore, it has good
immunity against noise and is able to communicate at relatively long distance (up to 1200 meters). However, it
also inherits the limitation of RS-485 which allows only a maximum of 32 devices to be connected to the same
communication line.
2.1
System Overview
A DMX512 system consists of one master device (transmitting device) connected to multiple slave devices
(receiving devices) in ‘daisy-chain’ manner as illustrated in Figure 1 below.
Figure 1
DMX512 System connected in Daisy Chain
A unique address must be assigned to each slave device by configuring the DIP switch embedded on each device.
The address may range from 1 to 512, depending on how many devices are connected and how many DMX512
slots/channels are consumed by each device. For example, an RGB-LED wallwasher may consume one DMX512
slot for each color. If its address is set at 10, it will consume slot 10, 11 and 12. The address for the next device
must be set to 13.
A termination resistance typically of 120Ω is connected at the furthest slave device to prevent signal reflection.
In the case where more than 32 devices are required in a system, an in-line device, such as optosplitter, can be
used.
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Overview of DMX512
2.2
Physical Layer
The standard specifies the physical layer of DMX512 to consist of the connector configuration and the circuit
topology. DMX512 system uses XLR-5 connectors, as shown in Figure 2. Transmitting device uses Ground
Referenced Topology while receving device uses Isolated Topology. In this document, only the physical layer of
the slave/receiving device is discussed.
2.2.1
XLR-5 Connector
Each receiving device has both a male and a female XLR-5 connector that is used for receiving and transmitting
the DMX512 signal, respectively. This is to create the daisy-chain topology that ensures the continuity of
communication from the transmitting device to the last receiving device.
Figure 2
XLR-5 Connector Pinouts. Male-type is on the left and Female-type is on the right.
The following Table 1 specifies the connections for the receiving device:
Table 1
DMX512 Pinout on XLR-5 Connector
Pin Number
Signal Name
Description
1
Common Reference
Data Link Common
2
Data 1+
Primary Data Link
3
Data 1-
4
Data 2+
5
Data 2-
Secondary Data Link (Optional)
In a typical DMX512 application, only Primary Data Link (DATA1+ and DATA1-) and Common Reference are
used.
The Secondary Data Link is not used and is reserved for future use. It is therefore common to find some lighting
fixtures that use XLR-3 connectors.
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Overview of DMX512
2.2.2
Isolated Topology
The standard specifies the use of isolated topology in the receiving device circuit, as illustrated in Figure 3 below.
This topology is not implemented in our solution, however users are encouraged to follow this topology strictly
when implementing their own solution. Refer to Figure 32 in the APPENDIX section for suggested circuit that fulfill
isolated topology.
Figure 3
Isolated Topology as specified in the standard
2.3
DMX512 Protocol
As the name suggests, there are 512 "pieces of information" carried in a DMX512 packet. Each "piece of
information" is also known as a slot or channel, which consists of 1 start bit, 8 data bits and 2 stop bits. A Reset
Sequence consisting BREAK, MAB and NULL Start Code must be transmitted before the slots.
Figure 4 illustrates a DMX512 packet.
Figure 4
DMX512 Protocol
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Overview of DMX512
The timing requirements for the receiving device are shown inTable 2.
Table 2
Timing Requirements for Receiving Device
Signal
Min. Value
Typ. Value Max. Value Description
Bit Rate
245 kbps
250 kbps
255 kbps
Bit Time
3.92 μs
4 μs
4.08 μs
BREAK
88 μs
176 μs
-
A falling edge transition followed by a low of at least 88 μs
followed by a rising edge.
MAB
8 μs
-
<1s
Mark After Break - The period of time measured from the
rising edge at the end of BREAK to the falling edge of the
start bit of the START Code.
MTBS
0
-
<1s
Mark Time Between Slot - The period measured from the
end of the second stop bit (bit 9) of the previous slot to the
falling edge of the start bit of the current slot.
MBB
0
-
<1s
Mark Before Break - The period measured from the end of
the second stop-bit of the last slot to the falling edge of the
next BREAK.
-
1.25 s
The period between two BREAKs
BREAK-TO- 1196 μs
BREAK
Application Note
Transmission rate for DMX512 protocol.
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DMX512 Implementation with XC836
3
DMX512 Implementation with XC836
Current solutions in the market use either a 16-bit or 32-bit microcontroller with a large memory size to implement
DMX512. The microcontroller receives and stores all the slots before processing them. This method is inefficient
as it requires 512 bytes of data memory while only a few are relevant to the receiving device. In addition, some
implementations use two or more pins because each IO pin can only support one function.
The implemented software stack described in this Application Note will selectively receive and store relevant slots.
This method reduces the required memory for the DMX512 software stack and gives more space for applicationspecific code. In addition, it will also be implemented on a single pin. This is possible because XC800 devices are
able to map multiple functions into a single IO pin.
The software stack will be implemented using Timer 2, UART and Timer 0. It will occupy 1.2KB of Flash and a few
bytes of RAM, depending on the number of required slots in the application.
Timer 2 and Timer 0 are 16-bit general purpose timers which are functionally compatible with the C501 product
family. Timer 2 has Capture Mode for pulse width measurement, which is useful to measure the width of BREAK
and MAB, while Timer 0 can be used to measure the BREAK-to-BREAK signal.
UART is an integrated communication peripheral that can be set as a 9-bit serial port to receive and validate the
START Code and the following slots.
3.1
Hardware
Figure 5 shows the DMX512 solution from Infineon. Aside from DMX512, the DALI (Digitally Addressable Lighting
Protocol) is also implemented on the board. This enables the evaluation of both lighting protocols on a single
platform by simply downloading a different protocol stack via the programming connector. The previous protocol
stack will be overwritten by the new one and the relevant circuitry will be activated after downloading.
Figure 5
Block Diagram and Actual Board
The connectors found on the board are the DMX512, DIP switches, power supply connector and SPD
(programming) connector.
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DMX512 Implementation with XC836
3.1.1
DMX512 Connectors
The DMX512 connector is shown in Figure 6 below. The differential DMX512 signal is received and converted to
TTL level by RS485 transceiver, where its Receive Output (RO) pin and Receive Enable (RE) pin are connected
to P2.7 and P0.6 of XC836, respectively.
In addition, there is a 120Ω termination resistance that must be enabled at the end of the daisy-chain connection
to avoid signal reflection. Users can enable this termination resistance by shorting the on-board jumper.
Figure 6
DMX512 Connector
3.1.2
DIP Switch
Each receiving device has embedded DIP switches to allow the user to assign a DMX512 address. In a typical
DMX512 application, 9-bit DIP switches are used. This allows an address range from 1 to 512. The user can set
the DIP switches to assign DMX Address 1 to 511, while address 512 is assigned by setting the DIP switches to
zero.
As a demonstration only board, our solution only uses a 4-bit DIP switch, where the supported address will range
from 1 to 16. Address 1 to 15 is achieved by setting the DIP switch and Address 16 is achieved by setting the DIP
switch to zero.
When an address higher than 16 is required, the user is able to set it by software, which will be explained in
Chapter 4.3.
Figure 7
4-bit on-board DIP switch
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DMX512 Implementation with XC836
3.1.3
Power Supply Connector and SPD Connector
5V DC is required at the power supply connector to power up the board. The programming connector (SPD) allows
the user to download the application code and the software stack using miniWiggler.
Figure 8
Power Supply Connector
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DMX512 Implementation with XC836
3.2
Software
The protocol stack utilizes three peripherals from XC836, namely Timer 2, UART and Timer 0 to receive and
process the DMX512 signal. It will validate and pass only the relevant slots to the application code.
This implementation demonstrates an RGB LED color control application where the protocol stack processes and
passes three slots of information to the application code. Another peripheral called CCU6 (Capture/Compare Unit
6), a PWM generator module, is also used to control the intensity of each LED color channel.
3.2.1
Software Abstraction Layers
Figure 9 shows the software abstraction layers which illustrate the processing of the DMX512 signal.
Figure 9
Software Abstraction Layer
When the DMX512 signal is received, its BREAK and MAB will be detected and verified by Timer 2. If the BREAK
and MAB fulfills the timing requirements, UART will then be activated to receive the START code and the slots.
The slots with an index number that matches the assigned DMX512 address will be stored temporarily.
BREAK-to-BREAK time is measured and validated using Timer 0. The temporary slot values are passed on to the
application code only if the packet's BREAK-to-BREAK time fulfills the required timing.
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DMX512 Implementation with XC836
3.2.2
Interrupt Timing Diagram
This process is summarized in Figure 10, the interrupt timing diagram.
Figure 10
Interrupt Timing Diagram
The verified slots will be passed on to the application code, which updates the CCU6 duty cycle registers with the
verified slots at a regular interval.
3.2.3
List of Source Code Files
The source code files used in the software stack are summarized in the following Table 3.
Table 3
List of Source Code Files for DMX512 Software Stack
Code Name
Description
DMX512_CONFIG.H
Contains Software Stack Defines and Configuration, e.g. DMX512 pin, RS485 Receive
Enable pin, number of required slots, etc.
MAIN.C
Contains hardware peripherals initialization, Valid Addres Check code and sample of
application code.
T2.C
Timer 2 initialization and Timer 2 External Interrupt subroutine (EXF2 flag) to detect
BREAK and MAB.
UART.C
UART Initialization, the interrupt subroutine (RI flag) to detect START code and slots,
reset sequence and Packet Length Check code.
T01.C
Timer 0 initialization and ISR to check for valid BREAK to BREAK time and Packet Loss
Handling code.
IO.C
GPIO initialization for the software stack. It follows the assigned DMX512 pin in the
DMX512_CONFIG.H
CC6.C
CCU6 peripheral initialization.
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3.2.4
Recommended DMX512 Signal Characteristics
The following Table 4 describes the recommended signal characteristics of the incoming DMX512 packet for the
implemented software stack.
Table 4
Recommended DMX512 Signal Characteristics
Signal
Recommended Value
Bit Rate
250 kbps
Bit Time
4 μs
BREAK
> 92 μs
MAB
> 12 μs
MTBS
> 8 μs
MBB
> 13 μs
BREAK-to-BREAK
> 1204 μs
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DMX512 Software Stack Configuration
4
DMX512 Software Stack Configuration
This chapter describes the configuration of the implemented software stack. All the settings can be found in
DMX512_Config.h
4.1
Configuring the Required DMX512 Slots
For an RGB color control application, there are at least three required DMX512 slots. Some other applications may
require a different number of slots. When this software stack is used for such applications, it can be configured to
receive a different number of slots, as shown in Figure 11 below.
Figure 11
Configuring Required DMX512 Slots
4.2
Alternative Pinouts
The implemented DMX512 software stack is designed to be portable across the XC800 microcontroller family and
offers alternative pinouts, as shown in Table 5 below.
Table 5
Alternative Pinouts for Various XC800 Devices
Device
Pin #
XC82x
P1.0
XC835
P1.0, P3.2
XC836
P1.0, P3.2, P2.7
The DMX512 pinout can be changed in DMX512_Config.h by typing the desired pinout after #define
DMX_AT_P2_7 to another pinout.
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DMX512 Software Stack Configuration
The following Figure 12 shows an example where the user changes the DMX512 pin to P3.2.
Figure 12
DMX512 Software Stack Configuration in DMX512_Config.h
When using P3.2 as the DMX512 pin, the SPD pin must be assigned to another pin. Refer to AP08108 for
programming the BMI value in the XC82x and XC83x devices.
4.3
DMX512 Address Setting by Software
The implemented DALI-DMX512 board supports an address range from 1 to 16. The address of the receiving
device can be set by software, by commenting the #define DIPSWITCH_ENABLE in DMX512_Config.h, then
uncommenting the #define SW_DMX_ADDRESS and adding the desired address, as shown in the Figure 13:
Figure 13
DMX512 Address Setting by Software
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Evaluating DALI - DMX512 Board for LED Color Control Application
5
Evaluating DALI - DMX512 Board for LED Color Control Application
The DALI-DMX512 Board from Infineon is a receiving or slave device that contains the two common lighting
protocols, DALI and DMX512. The board is designed to demonstrate an LED Color Control application on both
protocols. This chapter is intended as a step-by-step guide for users to evaluate this board.
5.1
Connecting the Boards in a Daisy-Chain
A simple twisted pair of shielded wires can be used to connect the boards. The diagram inserted in the top-left of
the following Figure 14 shows the wiring connection.
Figure 14
Two Boards connected in Daisy Chain
5.2
Setting the DMX512 Address with DIP switches
In a typical DMX512 device, the user can set the DMX512 address using DIP switch, where DIP switch #4 refers
to the Least Significant Bit (LSB) of the address. The following Figure 15 shows an example where the board is
set to Address 11.
Figure 15
Setting DMX512 Address to 4
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Evaluating DALI - DMX512 Board for LED Color Control Application
5.3
Connecting the Transmitting Device to the Daisy Chain
Once the address of each board is set, the transmitting device can be connected as shown in Figure 16.
Figure 16
Connecting Transmitting Device with Receiving Devices
5.4
Powering Up the Receiving Devices
Figure 17 shows the receiving devices being powered up from 5V power supply with on-board LED turned on.
Figure 17
Powering the Receiving Devices
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Evaluating DALI - DMX512 Board for LED Color Control Application
5.5
Powering Up the Transmitting Device from USB
The transmitting device requires 5V DC and is powered from USB, as shown in Figure 18.
Figure 18
Powering the Transmitting Device via USB
5.6
Controlling LED Color with the Transmitting Device
Figure 19 and Figure 20 show the touch pads and the 7-segment LED display functions on the transmitting
device.
Figure 19
XC836 Easy Kit Touch Pads
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Evaluating DALI - DMX512 Board for LED Color Control Application
Figure 20
7-Segment LED display functions
The LED to indicate transmission will only light up when there is a DMX512 signal transmission.
The following Table 6 describes the functionality of each touch pad.
Table 6
Touchpad Descriptions
Touchpad Name
Value Range Description
Next Address
0 - 24[DEC]
Go to next/previous slot address. For demonstration purposes, only
24 slots are supported by the transmitting device.
0 - FF [HEX]
Increase/Decrease current slot values. The value is represented as
hexadecimal.
Fine/Coarse
-
Adjust the resolution of Incr/Decr Slot Value. Selecting Coarse Mode
will modify the 2nd digit of Slot Value while Fine Mode will modify the
1st digit of the Slot Value. Default mode is Coarse Mode.
START/STOP DMX512
-
Start/Stop DMX512 Transmission
Next Scene
0 - 99 [DEC]
Go to the next/previous predefined scene.
-
Set the selected scene to the receiving devices. Pressing this button
will automatically enable the DMX512 transmission.
Prev Address
Incr Slot Value
Decr Slot Value
Prev Scene
Set Scene
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AP08131
Evaluating DALI - DMX512 Board for LED Color Control Application
The following Figure 21 shows the complete setup of DMX512 system for RGB-LED color control application.
Figure 21
Complete Setup of DMX512 System
The user can now control the LED color on each board from the transmitting device. For example, when the slot
value of address 04 is increased, the second board will display brighter red, while increasing the slot value of
address 08 will make the third board display brighter green. For more information on the transmitting device,
please refer to Application Note AP08132.
Application Note
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AP08131
Enhancement Features
6
Enhancement Features
The following features are implemented to enhance the reliability of the software stack while still complying with
the DMX512 standard.
6.1
Packet Length Check
The standard never specifies the minimum number of slots that must be transmitted, therefore it is common to find
some devices transmitting less than 512 slots. An error may be introduced to the receiving devices when the sum
of its assigned address and the number of required slots exceed the packet length. For example, a receiving
device with the address of 29 which requires 3 slots may have an error if the packet sent by the transmitting device
has only 30 slots. The receiving device will not be able to obtain the data for its third slot (slot 31).
This feature is implemented to make the software stack able to recognize the packet length of incoming DMX512
and adjust itself accordingly. Users do not have to worry about the packet length sent by the transmitting device.
Using the example above, the receiving device will turn itself off when it is unable to receive slot 31.
This feature works by sampling the packet length of the first few incoming packets. It will assign the maximum
value from the samples as the new packet length. By default, only the first four packets will be sampled by the
software stack. During this check, no data will be passed on to the application code. The subsequent packets
having a shorter or longer length will be considered as an error and will be discarded.
User can increase the number of packets to be checked by changing the PACKET_TO_BE_CHECKED in
DMX512_Config.h to more than four. Setting the value to 0 will make the software stack take the length of the first
received packet as the default packet length.
When this feature is disabled, the default packet length will be assumed as 513, i.e. START Code + 512 Slots.
Users, however, can define their own packet length by changing uwPacketLength value in MAIN.C, as shown in
Figure 23.
Figure 22
Packet Length Check Flowchart and its Code Snippet
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Enhancement Features
Figure 23
User-Defined Packet Length in MAIN.C
6.2
Valid Address Check
This feature is implemented to complement the Packet Length Check. After the packet length is known, it will
check whether the sum of DMX512 address and the required slots exceed the packet length. For example, when
a receiving device address is set to 30 while the received packet length is only 24, this will be recognized as an
error, and all hardware peripherals (Timer 2, UART and Timer 0) and the RS485 transceiver will be switched off.
In addition, when using 9-bit DIP switches as the mean for DMX addressing, the maximum achievable address is
only 511. On the other hand, when the DIP switches are not set, the receiving address will automatically be
assigned to zero, the NULL START Code, which has no practical value for the receiving device. This feature will
automatically set the address to 512 when the DIP switches are not set.
Figure 24
Valid Address Check Flowchart and its Code Snippet
Application Note
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AP08131
Summary
6.3
Packet Loss Handling
Packet loss may occur for several reasons, such as power failure at the transmitting device or because of a
disconnected communication cable. When there is no DMX512 signal received after 9.6 secs, the DMX512
software stack is reset and waits for the incoming DMX512 signal while still retaining the data before the packet
loss occured. The Packet Length Check feature will also reset to relearn the packet length.
Figure 25
Packet Loss Handling Flowchart and its Code Snippet
7
Summary
This application note has described the DMX512 solution from Infineon implemented on the XC836, an 8051based microcontroller. The DMX512 software stack is evaluated on an integrated DALI-DMX512 board, to also
allow evaluation of the DALI protocol.
Unlike other implementations in the market, the software stack selectively receives and stores only relevant slots.
This reduces the required memory size thus allowing for more complex application code. In addition, it is also
implemented on a single pin which will reduce the pinout requirements. The software stack is portable to other
XC800 devices and it also offers alternative pinouts.
Lastly, some additional features such as valid address check and packet length check are also implemented to
increase the reliability of the software stack while maintaining compliance with the standard.
Application Note
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AP08131
References
8
References
[1]
ANSI ESTA E1.11 - 2008 “Asynchronous Serial Digital Data Transmission Standard for Controlling Lighting
Equipment and Accessories”
[2]
XC82x User Manual version 1.2
[3]
XC83x User Manual version 1.1
[4]
AP08108 “Programming the BMI Value in the XC82x and XC83x Products”
[5]
AP08132 “DMX512 Transmitting Device using XC836”
[6]
AP08102 “DALI Control Gear Software Stack”
[7]
AP08114 “DALI Control Device using XC836”
[8]
AP08104 “Guide to using the DALI LightNet Tool”
[9]
AP08105 “DALI Demo using Touch Sense Control”
Application Note
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AP08131
References
Appendix - DALI-DMX512 Board Schematic
Figure 26 and Figure 27 show the schematic of DALI-DMX512 Board.
Figure 26
DALI-DMX512 Board Schematic - DALI/DMX512 PHY
Application Note
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References
Figure 27
DALI-DMX512 Board Schematic - XC836 and RGB LED
Application Note
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AP08131
References
Figure 28
DALI-DMX512 Board Layout
Application Note
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AP08131
References
Appendix - DMX512 Software Stack Flowchart
The following Figure 29, Figure 30 and Figure 31 shows the flowchart from each peripheral that is used to create
the DMX512 software stack.
Timer 2 External Interrupt
T2 External Interrupt occurs
Clear Interrupt Flag
Rising edge of MAB is detected
Y
Turn on Timer 0 for BREAK‐
to‐BREAK measurement
Get previous packet BREAK‐to‐
BREAK time
N
Falling edge of slot start‐bit is detected
Y
Get BREAK timing from T2 register
Get MAB time from T2 register
Y
Stop Timer 2
Enable UART
Y
Disable Timer 2 external interrupt
Reset slot counter
Set Timer 2 to start at falling edge and interrupt at rising edge
Valid BREAK‐to‐BREAK & known packet length & valid temp data
N
N
Disable UART Receiver
Set next interrupt to detect falling edge of start‐bit
Proceed to detect slot
N
Stop Timer 2 and Reset Timer 2 register
Valid MAB
Valid BREAK
Disable Timer 0 and reload its register
Y
Reset BREAK‐to‐
BREAK count
Reset BREAK‐
to‐BREAK time Register
Get DMX data from temporary buffer
Clear valid temp data bit
Proceed to receive slot
N
Set Timer 2 to start at falling edge and interrupt at rising edge
Disable Timer 0 and reload its register
Reset state
Return
Figure 29
Timer 2 Flowchart
Application Note
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References
UART Interrupt
UART frame received
Packet Length Check
Reset DMX512
Record packet length from slot counter
Disable UART Interrupt
Clear RI flag
N
Reset Timer 2
Valid Bit‐8 (one of the stop bits)
N
Known packet length bit
Y
Packet Length Check
Reset DMX512
Reset DMX512
N
Y
Clear Valid Temp Data bit
Y
Slot counter == 0
Sample > temporary max value
Disable Timer 0 and reset the registers
N
Slot counter > 0
Y
Y
Valid START Code
Known packet length && ADDRESS < Slot Counter < (ADDRESS + REQUIRED SLOTS)
N
Reset DMX512
Slot Counter < ADDRESS or Slot Counter > (ADDRESS + REQUIRED SLOTS)
N
Reset state
Temporary Max Value = Sample Value
Return
Reset slot counter
N
Slot Counter ==
Packet Length
Store DMX Data in temp variables
Y
Y
Increase Slot Counter
Reset DMX512
Increase Slot Counter
Return
Figure 30
Y
Packet length = temporary max value
Set Valid Temp Data bit
Increase Slot Counter
Increment sample count
Sample count >= number of packet to be checked
Y
Y
N
N
Set known packet length bit
Return
UART Flowchart
Timer 0 Interrupt
Timer 0 Interrupt occurs
Reload Timer 0
Increase counter
Counter reaches 9.6 sec
Y
Packet Loss Handling
N
Return
Figure 31
Timer 0 Flowchart
Application Note
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References
Appendix - Suggested Circuit to Fulfill Isolated Topology Requirement
As mentioned in Section 2.2.2, the standard requires all receiving devices to be implemented using isolated
topology. The following Figure 32 shows a suggested circuit using isolated topology for DMX512 Receiving
Device.
Figure 32
Suggested Isolated Circuit for DMX512 Receiving Device
Application Note
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Published by Infineon Technologies AG
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