AN4460 datasheet(22/54 Pages) STMICROELECTRONICS

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Firmware implementation

AN4460

22/54

DocID026129 Rev 1

Figure 7. Dimming channel relation

5.2

Firmware evolution

The following section describes the software timing characteristics as shown in Figure 8.

Figure 8 shows the relationship between two consecutive STMR_ISR() routines and the

other principal subroutines. The colors define if the routines run in interrupt mode (colored)

or are called from main (black). The PMW1_ON line is the dimming period: when the line is

high, the PWM signal is high too.

Figure 8. FW timeline evolution

The lines are here described:



STMR_ISR(): STMR timer interrupt.

The STMR timer has a granularity of 20 µs (STMR unit). The timer is used to start

and stop the dimming period for each SMED and triggers the SWx bit on the MSC

SMSWEV register. On every interrupt, the timer is reprogrammed so that the next

1/200 Hz = 5 mS

DIMM1

time

DIMM2

DIMM3

DIMM4

1/200 Hz = 5 mS

AM16707v1

1/200 Hz = 5 mS

PWM _

1ON

time

ADC_ISR()

Get_Key()

STMR_ISR()

Not in scale

Comp_PWM ()

SMEDx_ISR()

Comp_DUTY()

AWU time

AM16708v1

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