How to use an oscilloscope to analyze the DALI protocol?

With the rapid development of building automation and lighting industry, traditional lighting control is gradually replaced by intelligent control. DALI, as a new intelligent lighting control protocol, defines the communication method between electronic ballast and controller to realize the automatic control of intelligent lighting system. So, how to quickly debug the DALI protocol of lighting control?

1. DALI Introduction

DALI Digital Addressable Lighting Interface ballast is the latest dimmable fluorescent lamp ballast. DALI is a data transmission protocol that defines the communication method between electronic ballast and device controller. The system based on DALI protocol has distributed intelligent modules. Each intelligent DALI module has digital control and digital communication capabilities. The address and lighting scene information are stored in the memory of each DALI module. DALI modules communicate digitally, transmit instructions and status information through the DALI bus, and realize functions such as light switching, dimming control, and system settings. The DALI bus develops a lighting control system with a simple system structure, easy installation, easy operation, and excellent functions. It can be used for lighting control in a room, and can also be connected to more advanced device networks, such as Ethernet, to support more devices and sufficient network bandwidth. The basic parameters of the DALI protocol are as follows:

Figure 1 Basic parameters of DALI protocol

DALI bus is mainly used for dimming control of multiple fluorescent lamps and LED lighting. Each ballast can be addressed separately through the dimming controller. A single-segment DALI digital control line can address 64 ballasts separately. 16 lighting scenes can be set in each ballast. The same ballast can also be grouped in one or more groups. The maximum number of groups is 16, that is, a DALI system can control up to 1,000 ballasts.

Figure 2 DALI system structure diagram

2. DALI data frame structure

DALI uses bidirectional Manchester encoding, and the values ​​"1" and "0" represent transitions of two different levels. A transition from a logic low level to a high level is represented as "1", and a transition from a logic high level to a low level is represented as "0".

Figure 3 Schematic diagram of DALI level standard

DALI data is divided into two categories: forward frames and backward frames. The transmission direction of the forward frame is from the master control unit to the slave control unit, and it consists of 19 bits, including 1 start bit, 8 address bits, 8 data bits and 2 stop bits, as shown in Figure 4;

Figure 4 DALI forward frame structure

Start bit: logical value "1" is used as the start bit

· Address bit: 8-bit address bit can be used to realize communication between each electronic ballast in the system, and control the individual address of a single slave separately. The addressing range is 0-63, and 64 different addresses can be controlled, which is called short address; DALI controller has group address instructions for group control. The addressing range is 0-15, and up to 16 groups can be controlled in groups.

Data bit: The function of transmitting information in both forward and reverse directions of 8 data bits, including control information such as turning lights on/off, dimming of lights and dimming time.

· Stop bits: two non-encoded high levels.

The transmission direction of the backward frame is from the slave control unit to the master control unit. In the DALI protocol, the slave sends data to the master only when the master controller queries it. The data sent by the slave to the master consists of 11 bits of data, the first bit is the start bit, the 2nd to 9th bits are data bits, and the 10th and 11th bits are stop bits. As shown in Figure 5.

Figure 5 DALI backward frame structure

3. Field Application and Analysis

The DALI communication protocol for lighting control is simulated on site. Here, the data mining oscilloscope ZDS4054 Plus is used as an example. Its free standard DALI protocol decoding function can decode the data of the full memory 512Mpts, and can monitor the signal between the lighting controller and the ballast. The information of one frame of data can be viewed in the event table, as shown in Figure 6 below:

Figure 6 DALI protocol decoding interface

To perform abnormal analysis on data monitored over a long period of time, you can use the dual ZOOM multi-window display function in the zoom mode of the oscilloscope to perform multi-window abnormal monitoring and analysis of the signal. You can analyze the details of any data frame and the rising or falling edge of the data frame at the same time, and then by viewing the details of the enlarged data, the data and waveform in the event table correspond one by one, which makes it very convenient to locate the abnormality, as shown in Figure 7 below.

Figure 7 Detailed analysis

IV. Conclusion

The ZDS4054Plus oscilloscope comes with the DALI protocol as standard for free. Based on the 512Mpts storage depth, it can monitor and decode the lighting control DALI communication for a long time and support DALI protocol triggering. At the same time, the oscilloscope's rich plug-ins and abnormal search methods can be used to analyze waveform details and quickly locate problems.