AN2316 - Application Note

ST7FLITE05 Software Description

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4.1

Peripheral Initialization

The peripherals are initialized. After initialization, the firmware waits 255ms for the hardware

to be start up. The potentiometer is read, and the digital values are used to compute those

to be loaded into the successive DCR registers. Initialization activities include the following:

4.1.1

Auto-reload Timer (AT) Configuration

The 12-bit AT is configured in PWM mode so that the ATR registers contain the auto-reload

value used to set the PWM frequency.

4.1.2

PWM Duty Cycle, Overflow and Compare Interrupts

The PWM frequency and the DCR registers contain the value which sets the PWM duty

cycle.

Furthermore, the PWM output on the ATPW0 pin is enabled by setting the OE0 Bit in the

PWMCR register, and both, the overflow and compare interrupts have been enabled.

Note:

In order to guarantee the proper operation of the overall system, using very high and very

low duty cycle values are discouraged.

If the duty cycle exceeds a higher threshold, the PWM must be switched off and the

microcontroller pin must be kept continuously in logic high state. The PWM output is

enabled again only if the user turns the potentiometer so the corresponding duty cycle is

below the higher threshold minus hysteresis (see Figure 9 on page 16).

If the duty cycle goes below a lower threshold, the PWM must be switched off and the

microcontroller pin must kept continuously in logic low state. The PWM output is enabled

again only if the duty cycle related to the potentiometer position goes above the lower

threshold plus hysteresis (see Figure 9).

4.1.3

ST7LITE Timer

The 8-bit LITE Timer is configured so that an overflow event (and the related interrupt)

occurs every millisecond. This allows users to have a time base at their disposal to

implement, for example, the soft variation of the PWM duty cycle.

4.1.4

Channel 0 A/D Conversion