AN4121

Circuit description

Doc ID 023243 Rev 1

9/26

In standalone operating mode these multipurpose pins output:

●

negative power direction on SYN-NP pin;

●

tamper condition detected on SDA-TD pin;

●

no load condition detected on SCL-NLC pin.

For this reason these pins are connected to the three LEDs, D9, D10 and D11.

In this configuration, the LED pin outputs a pulse train with frequency proportional to the

three-phase power and it is connected to LED D12.

When configured in peripheral operating mode, the SPI port is enabled and some

microcontroller based applications can either read internal data records or write the mode

and configuration signals by means of dedicated protocol, or reset the device.

By default, the STPMC1 is configured in peripheral mode (configuration bits APL=0).

This also implies the following output settings:

●

watchdog reset signal on MON pin;

●

zero-crossing (ZCR) on MOP pin;

●

programmable energy pulsed output on LED pin.

For further information on STPMC1 programmable bit settings, please refer to the

datasheet.

The STPMC1 SPI protocol is explained in detail in a related application note.

Connector P1 is also used in the demonstration phase to connect the measurement module

to a PC through the STPM parallel programmer/reader hardware interface.

This allows the user to set temporary and/or permanently the internal STPMC1 registers

using a dedicated GUI.

The VOTP pin on the connector P1 is used when a host wants to permanently write some

configuration bits in the STPMC1 device. In this case, a +15 V power level must be present

on the VOTP. This level must be delivered from the host itself because the module does not

have an onboard charge pump.

Table 6.

P1 connector pin description

Pin

Pin name

Functional description

1.

VOTP

Power supply input of +15.0 V during permanent write to OTP cells

2.

---

Not connected

3.

GND

Signal reference level 0 V and power supply return

4.

SDA-TD

SPI interface data

5.

SCS

SPI interface enable

6.

SCL-NLC

SPI interface clock

7.

---

Not connected

8.

SYN-NP

SPI interface signal

9.

---

Not connected

10.

VCC

Power-out of +3.3 or 5 V