AN2799

Functional description

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3

Functional description

The STPM01 host interface is a single bidirectional data line SPI with a 32 MHz maximum

read speed and 100 kHz maximum write speed. Due to these requirements the STM32

microcontroller is used in the following way:

●

In the reading phase, the MISO and SCLK pins are configured in alternate functions

and used by the SPI2 peripheral. The maximum reading speed is 18 MHz by an APB

speed equal to 36 MHz, configuring the SPI baud rate with APB/2.

●

In the writing phase the MISO and SCLK pins are configured as GPIOs and the SPI

operation is emulated by firmware controlling the speed operations to not exceed the

100 kHz writing speed limit. The MCO pin is configured to provide the HSE clock.

4

Firmware description

The firmware for the management of the STPM01 energy meter has been developed using

an object oriented programming (OOP) approach even if standard ANSI C programming

language has been used.

4.1

Power meter object description

The power meter object is defined and implemented in the PowerMeterObj.c,

PowerMeterObj.h and PowerMeterTypes.h files. The power meter is represented by a

structure containing the properties and the method of the Power Meter Object as illustrated

in

Figure 3.

Figure 3.

Power meter object

AM00078v1