AN2841

Dimming application using an STM32 microcontroller

11/31

Figure 8.

Conversion of

LEDmap array to LEDdriverDATAbuffer

Example using a 4×8 LED matrix with an 8-bit PWM resolution

while(1)

for(depth = 1; depth<=0xff; depth++){

for(DATAchar = 0; DATAchar < 4; DATAchar++){

for(outputBIT = 0; outputBIT < 8; outputBIT++){

LEDdriverDATAbuffer[DATAchar] <<= 1;

if(LEDmap[(DATAchar*8) + outputBIT] > depth)

LEDdriverDATAbuffer[DATAchar] |= 0x0001;

else

LEDdriverDATAbuffer[DATAchar] &= 0xFFFE;

}

SPI_SendData(SPI1, LEDdriverDATAbuffer[DATAchar]);

}

LE_LOW();

LE_HIGH();

LE_LOW();

}

Even though the dynamic data preparation consumes a minimum of system memory, it

takes a lot of computational time. This approach is only recommended for low LED count

applications. A dynamic data preparation approach can reach 100 Hz for 32 LEDs (with

maximum code optimization in C compiler on the STM32 evaluation board).

LEDmap[0] > depth =

0

LEDmap[1] > depth =

1

LEDmap[2] > depth =

1

LEDmap[3] > depth =

0

LEDmap[4] > depth =

1

LEDmap[6] > depth =

1

LEDmap[7] > depth =

0

LEDmap[8] > depth =

0

for one time stamp depth = 50

LEDmap= { 20, 60, 75, 22, 100, 255, 0, 5}

LEDdriverDATAbuffer[0]

LED driver

for outputBIT from 0 to 7

SPI

AM00347