AN2383 datasheet(28/39 Pages) STMICROELECTRONICS

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Software management

AN2383

28/39

Doc ID 12433 Rev 3

Software management

The MCU has to process six types of events: pot-on-plate detection, temperature, keyboard

scan, display refresh and current control. These events are processed every 20

milliseconds; in fact, they are synchronized with the zero voltage switching signal.

The ZVS circuitry generates a square wave with a frequency of 50 Hz. The signal is sent to

the ei1 MCU pin, which is configured as an external interrupt input for both rising and falling

edges. Therefore, an MCU interrupt is generated every time a falling edge or a rising edge

occurs on the pin.

Figure 18.

The six most important software events

The first event, shown in Figure 18 as number 1, takes place as soon as the interrupt

triggered by a rising edge on the ZVS signal occurs. Pot-on-plate detection is performed by

sampling the voltage drop on the VLINK signal during this time.

Before another interrupt occurs, there is still a lot of time to handle three other events.

Events 2 and 3 monitor the temperature of the heatsink and the plate respectively. During

event number 4, the keyboard is scanned to check if a key has been pressed (or released).

A software anti-bounce has been implemented to avoid undesired conditions.

Event number 5 takes place immediately after the interrupt generated by a falling edge of

the ZVS signal occurs. The display refresh routine is performed.

During the last event, number 6, the I-CTRL signal is scanned and compared to the look-up

table that the software refers to for each working level. If any discrepancy appears between

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