Dimming application using an STM32 microcontroller

AN2841

20/31

3.2.2

Reduced lookup table (non redundant)

Only the data that changes the LED driver output state is generated. A LED can change the

state only once per complete PWM cycle: from one to zero. If there are i number of LEDs,

there are i new data items for the LED drivers. For example, if i = 32 LEDs when using an

8-bit PWM, you need a cycle with i × i = 32 × 32 = 1024 loops.

The inside of the loop is the same for full lookup table generation as described in

Section 3.2.1. The lookup table row is computed only in case you need to change the LED

intensity pattern (specific value of a parallel output configuration). Table 3, Table 4 and

Table 5 bring better understanding of the lookup table reduction. The C code of the reduced

lookup table generation is shown in the example below.

Table 2.

Full lookup table

Step

Output

LED 1

LED 2

LED 3

…

…

LED i

0

11

1

1

1

11

1

1

2

11

1

1

3

01

1

1

4

01

1

1

5

01

0

1

6

01

0

1

…

00

0

1

…

00

0

1

00

0

1