Design and Implementation of Two LONWORKS Frequency Acquisition Nodes

1. Introduction In recent years, LONWORKS measurement and control network technology has gained significant popularity across various fieldbus applications. It is widely adopted in systems such as SCADA (Supervisory Control and Data Acquisition), industrial automation, building management, and intelligent transportation. The core of implementing a LONWORKS-based system lies in the development of intelligent nodes that can effectively communicate and process data. This paper presents two distinct design and implementation approaches for LONWORKS frequency acquisition nodes, offering a detailed comparison of their respective advantages and disadvantages to guide future development choices. 2. LONWORKS Intelligent Node The central component of a LONWORKS intelligent node is the NEURON chip, typically either the NEURON 3120 or NEURON 3150. These chips feature a unique internal architecture with three integrated CPUs: CPU-1 serves as the medium access controller, CPU-2 functions as the network processor, and together they handle all communication tasks. CPU-3 acts as the application processor, responsible for executing user-written code and system commands. There are two common structural configurations for LONWORKS nodes. One uses the NEURON chip as the central unit, managing both communication and application tasks, as illustrated in Figure 1(a). The other employs a MIP (Main Processor) structure, where the NEURON chip solely handles communication, while the main processor runs the application logic, as shown in Figure 1(b). ECHELON has integrated the dual-line transceiver FTT-10A with the original NEURON chip. More recently, the FT3150 and FT3120 dual-line intelligent transceivers were introduced. These newer chips maintain compatibility with the original 3150 design, simplifying peripheral circuit development and reducing both time and cost. This compatibility also enhances the node's resistance to interference. Additionally, the FT3150 and FT3120 support higher input clock speeds, up to 40 MHz, significantly boosting processing performance. As a result, the design in this paper replaces the traditional NEURON chip and transceiver with the FT3150, leading to a more streamlined and efficient node structure. 3. Design of Frequency Acquisition Node Based on NEURON Chip LONWORKS is specifically designed for industrial measurement and control applications. The NEURON chip provides 11 I/O ports, which can be programmed to define up to 34 application objects. Among these, the cycle input object, pulse count object, and total input object are particularly useful for measuring frequency signals from the field. Below are some basic applications of these three types of I/O objects: The cycle input object measures the time interval between two rising edges or two falling edges of an input signal. A simple example is shown below: [Image: Periodic Input Object Example] When using a 10 MHz crystal oscillator with the FT3150, the resolution of the cycle input object reaches 25.6 microseconds. The pulse count object measures the average frequency of the input signal over a period of 0.8388608 seconds by counting the number of signal edges. An example of its use is as follows: [Image: Pulse Count Object Example]

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