November 2010

Doc ID 17783 Rev 1

1/24

AN3254

Application note

SPI protocol for the STPMC1 metering device

Introduction

The STPMC1 device is an ASSP designed for effective measurement in power line systems

utilizing the Rogowski coil, current transformer, and shunt or Hall current sensors. Used in

combination with one or more STPMSx ICs, it implements all the functions needed in a 1, 2,

or 3-phase energy meter. It can be coupled with a microprocessor for multifunction energy

meter or it can directly drive a stepper motor for a simple active energy meter.

All the data measured by the STPMC1 are accessible through the SPI port, which is also

used to configure and calibrate the device. The configuration and calibration data are

retained in a 112-bit OTP block; in any case, these data can be dynamically changed in

microprocessor based meters.

instantaneous voltage and current, line frequency, phase status, etc.) should be read by the

microcontroller at a fixed time interval to be further processed.

This application note describes the SPI protocol to read measured data from the STPMC1

in a multiphase energy meter and how these readings should be processed by the

application.

For more details on the device please refer to the STPMC1; Programmable poly-phase

energy calculator IC, datasheet.

Figure 1.

STPMC1 based application block diagram

Current

Sensor

Current

Sensor

Current

Sensor

Voltage

Sensor

Voltage

Sensor

Voltage

Sensor

Current

Sensor

S TPMS1

S TPMS1

S TPMS1

S TPMS1

STPMC1

DAR

DAS

DAH

DAN

DAT

(

(

MCU

Application Support and

Pe riphera l Control

MCU

Applica tion Support and

Pe riphera l Control

SPI

MCU

Application Support and

Pe riphera l Control

MCU

Applica tion Support and

Pe riphera l Control

SPI

4 wire s

Step pe r C ounter

Step pe r C ounter

LE D ind ica tors

www.st.com