AN3254 Datasheet, PDF (1/24 Pages) STMicroelectronics – SPI protocol for the STPMC1 metering device

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.
Measured data (like active and reactive energy, total and per phase, phase V_RMS, I_RMS and
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
N R ST
Current
Sensor
Voltage
Sensor
Current
Sensor
Voltage
Sensor
Current
Sensor
Voltage
Sensor
Current
Sensor
S TP MS 1
S TP MS 1
S TP MS 1
S TP MS 1
LE D ind ica tor s
S tep pe r C ou n ter
DAR
(^DAS
(^{DAT STPMC1}
DAN
DAH
4 wires
SPI
MMCCUU
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PPeerripiphheerraal _{lCCoonnttrrool l}
November 2010
Doc ID 17783 Rev 1
1/24
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