This article describes a system that implements a power line modem from software and hardware in compliance with the CEA709 protocol using a fixed-point DSP controller (TMS320LF2812). The specific design method of the analog terminal is described in this paper, and this terminal is necessary for the stable transmission and reception operation process.
1 System framework based on CEA709 protocol
Figure 1 shows the physical block diagram of the ANSI/CEA709 protocol standard.
Figure 1 CEA709 protocol physical layer block diagram
LonWorks, a widely used control network platform in the fields of rail transit, network energy management, intelligent buildings, HVAC, coal mine safety, energy and environmental management, has become the guiding technical document of China's national standards. The global building, home, industrial and transportation automation industries are currently heavily based on the LonWorks platform. The LonWorks platform is the core technology platform for the world's largest residential smart meter network. It is used by smart meters for residential and small commercial electricity meters in countries such as Sweden, the Netherlands and Australia. The protocol running on this platform is the US control network standard ANSI/ CEA709. At present, more and more Chinese manufacturers and integrators have adopted the ANSI/CEA709 protocol standard, for example, on the Qinghai-Tibet Railway, the world's longest high-altitude railway train, using the LonWorks technology platform, using the ANSI/CEA709 protocol. Used for technical monitoring and control of various systems, including monitoring of the most advanced passenger oxygen supply systems.
For the CEA709 physical layer block diagram in Figure 1, the system block diagram of the DSP to implement the CEA709 modem function is shown in Figure 2. The DSP (TMS320F2812) has 150 MIPS of computing power. The signal acquisition uses a 12-bit on-chip analog-to-digital converter with a conversion speed of 12 Msps. The DSP provides multiple PWMs to accommodate the power line modem.
Figure 2 system block diagram
Two on-chip PWM outputs and one line driver are used to implement the modem's transmit function. An A/D input is used to sample the bandpass input port signal to implement the receiver's receive function. The bandpass filter is actually a discrete filter. They complete the analog front end design of the interface with the AC blocking capacitor and the coupling transformer.
The following mainly introduces the design process of the analog front-end interface.
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