AN2159

SPI module description

Doc ID 11400 Rev 3

5/23

The best way to connect this standard SPI port to the STPMxx SPI is to have SCS and SYN

driven from some general purpose i/o port and SCL and SDA driven from SPI pins.

The suggested connection between microcontroller and STPMxx is the following:

●

MISO connected to SDA;

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MOSI not connected;

●

SCLK connected to SCL;

●

SS connected to SCS;

●

a general purpose I/O pin connected to SYN.

In this way the SPI peripheral unit of microprocessor should operate as 2-wire (simplex

synchronous transfers) SPI.

The micro SPI peripheral can be used during STPMxx device reading, while during the

writing process it is possible to implement the SPI protocol via firmware.

In fact, in real applications with STPM01 the meter is calibrated and configured during meter

production, so the main microcontroller task is to read from the device and, more rarely, to

reset the device.

In STPM10 based meters the metering device has to be configured at startup from the

microcontroller, but also in this case the writing process is done once a while, while reading

is a continuous process during meter lifetime.

In both cases, since the reading time is crucial for a correct evaluation of the device data, it

is advisable to emulate writing procedure by firmware and to read using SPI peripheral

functionality, thus exploiting all the port performances to reach very fast reading.