MEC1404 Datasheet, PDF (392/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
FIGURE 28-5:
300
LINEAR BRIGHTNESS CURVE EXAMPLE
250
200
Cycle150
Duty
100
50
0
0 _{320 640 960 1280 1600 1920 2240 2560 2880 3200 3520 3840 4160 4480 4800 5120 5440 5760 6080 6400 6720 7040 7360 7680 0008 8320 8640 8960 9280 9600 9920 10240 10560 10880}
Time in ms
28.9.3.2 Non-linear LED brightness change
In this example, the brightness of the LED increases and diminishes in a non-linear fashion. The brightness forms a
curve that is approximated by four piece wise-linear line segments. The entire cycle takes about 2.8 seconds. The rise
time and fall time are about 1 second, with a hold time at maximum brightness of 320ms and a hold time at minimum
brightness of 400ms. The LED brightness varies between full off and full on. The PWM size is set to 7-bit, so the time
unit for adjusting the PWM is approximately 4ms. The registers are configured as follows:
TABLE 28-10: NON-LINEAR EXAMPLE CONFIGURATION
Field
PSIZE
MAX
MIN
HD
LD
Duty cycle most
significant bits
LED_INT
LED_STEP
7-bit
255 (effectively 127)
0
80 ticks (320ms)
100 ticks (400ms)
000b
001b
010b
2
3
6
4
4
4
Value
011b
6
4
100b
9
4
101b
9
4
110b
16
4
1110
16
4
DS00001956D-page 392
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