MEC1404 Datasheet, PDF (391/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
The frequency of the PWM pulse waveform is determined by the formula:
f_PWM = _---2---5---6----_--^f--^c-_-^l--_L^o---^c_D--^k----+-----1----_--_
where f_PWM is the frequency of the PWM, f_clock is the frequency of the input clock (32.768 KHz clock or 48 MHz clock)
and LD is the contents of the LD field.
Note:
At a duty cycle value of 00h (in the MIN register), the LED output is fully off. At a duty cycle value of 255h,
the LED output is fully on. Alternatively, In order to force the LED to be fully on, firmware can set the CON-
TROL field of the Configuration register to 3 (always on).
The other registers in the block do not affect the PWM or the LED output in Blinking/PWM mode.
28.9.3 BREATHING EXAMPLES
28.9.3.1 Linear LED brightness change
In this example, the brightness of the LED increases and diminishes in a linear fashion. The entire cycle takes 5 sec-
onds. The rise time and fall time are 1.6 seconds, with a hold time at maximum brightness of 200ms and a hold time at
minimum brightness of 1.6 seconds. The LED brightness varies between full off and full on. The PWM size is set to 8-
bit, so the time unit for adjusting the PWM is approximately 8ms. The registers are configured as follows:
TABLE 28-9: LINEAR EXAMPLE CONFIGURATION
Field
PSIZE
MAX
MIN
HD
LD
Duty cycle most
significant bits
LED_INT
LED_STEP
8-bit
255
0
25 ticks (200ms)
200 ticks (1.6s)
000b
001b
8
8
10
10
010b
8
10
Value
011b
8
10
100b
8
10
101b
8
10
110b
8
10
1110
8
10
 2015 - 2016 Microchip Technology Inc.
DS00001956D-page 391