Design and Implementation of Two LONWORKS Frequency Acquisition Nodes

1 Introduction

In recent years, LONWORKS measurement and control network technology has sprung up in many fieldbuses, and it is widely used in data acquisition and monitoring systems (SCADA), industrial control, building automation, intelligent transportation and other fields. The key to implementing the LONWORKS measurement and control network is the development of the LONWORKS intelligent node. This paper proposes two design and implementation methods of LONWORKS frequency acquisition nodes , and comprehensively compares the advantages and disadvantages of the two.

2. LONWORKS intelligent node

The core processor neuron chip of the LONWORKS intelligent node is NEURON 3120 or NEURON3150. The neuron chip has a unique internal structure: three CPUs are integrated inside the chip, CPU-1 is the medium access controller, and CPU-2 is the network processor. The two together complete the network communication function of the node, and the CPU-3 is an application processor, and is mainly responsible for executing the code written by the user and the operating system command invoked by the user code. There are two types of structures for a typical LONWORKS intelligent node. One is a node with a NEURON chip as its core. The NEURON chip handles both user applications and network communication, as shown in Figure 1(a). The other is a node with MIP structure. The NEURON chip only acts as a communication processor and node. The application is executed by the main processor, as shown in Figure 1(b).

ECHELON has integrated the dual-line transceiver FTT-10A with the original neuron chip. Recently, the dual-line intelligent transceiver FT3150 and FT3120 chips have been introduced. The new FT3150 and FT3120 chips are compatible with the original 3150 chip in the design of peripheral circuits, which saves the user time spent on peripheral circuit design, which not only reduces the development difficulty and development cost of the node, but also improves the node. Anti-interference. In addition, the FT3150 and FT3120 chips also support higher input clocks, with a maximum input clock of up to 40M Hz, which greatly increases the processing speed of the entire chip. Therefore, the design uses FT3150 chip instead of NEURON chip and transceiver in Figure 1, the structure of the node is simpler.

3. Design of frequency acquisition node based on neuron chip

LONWORKS is a control network dedicated to the field of industrial measurement and control. In order to facilitate the use of 11 I/O ports of the NEURON chip, it can be programmed to define 34 application objects. The cycle input object, the pulse count object, and the total number of input objects can all measure the field frequency signal. The following is a simple application of these three types of IO objects:

The periodic input object measures the time interval between two rising edges or two falling edges of the input signal. The simple application is as follows:

When the FT3150 uses a 10M crystal oscillator, the resolution of the periodic input object is 25.6us. The pulse count input object can measure the average frequency of the input signal through the input edge of the technology 0.8388608s. The simple application is as follows:

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