AN3975

System

Doc ID 022170 Rev 1

5/26

2

System

2.1

System description

The system being described contains two basic parts:

Power meter part: An interface to a power meter that can communicate with superior

system over RS485.

PC part: An interface that can communicate with the PC (using a USB connection) that is

a superior system for the power meter.

Both interfaces are interconnected by a power line link using the ST7590 demonstration

board. Once there are some data to be sent to the power meter, the PC sends this data to

the USB Virtual COM port. In this system, the microcontroller (PC part) takes the data from

the USB, encapsulates it into the commands for the first power line modem (base node) and

sends it to the power line. Another modem reads the data coming from the power line

(service node), and sends them to the microcontroller, power meter part. The

microcontroller extracts the data from the power line modem and sends them to UART_A.

The RS485 driver is connected to UART_A, so the data sent to the UART_A are converted

to RS485 and these data are delivered to the power meter. If the power meter replies, the

data comes back through this channel to the PC.

The microcontroller module used in this application is the connectivity gateway (STEVAL-

PCC012V1). This module is referred to as CG in the following text.

2.2

System specification

Power meter part (see Figure 1 and Figure 7)

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Power meter with RS485 terminals. Two terminals (+, -) for half duplex RS485

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Line driver for RS485 to UART_A

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Connectivity gateway system with STM32 interfacing RS485 via UART_A

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Connectivity gateway system with STM32 interfacing ST75xx via UART_B

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PLM ST75xx using UART_B and connection to power lines

PC part (see Figure 1)

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PC with USB

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Connectivity gateway system with STM32 offering USB connection providing Virtual

COM port functionality.

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Connectivity gateway system with STM32 interfacing ST75xx via UART_B

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PLM ST75xx using UART_B and connection to power lines

Modulation and modem specifications

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ST7590, OFDM modulation, PRIME protocol, one logical channel opened by service

node.