ST7FLITE02 STMICROELECTRONICS [STMicroelectronics], ST7FLITE02 Datasheet - Page 55

• Manufacturer Part Number: ST7FLITE02
• Description: 8-BIT MICROCONTROLLER WITH SINGLE VOLTAGE FLASH MEMORY, DATA EEPROM, ADC, TIMERS, SPI
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

12-BIT AUTORELOAD TIMER (Cont’d)
11.2.3 Functional Description
PWM Mode
This mode allows a Pulse Width Modulated sig-
nals to be generated on the PWM0 output pin with
minimum core processing overhead. The PWM0
output signal can be enabled or disabled using the
OE0 bit in the PWMCR register. When this bit is
set the PWM I/O pin is configured as output push-
pull alternate function.
Note: CMPF0 is available in PWM mode (see
PWM0CSR description on
PWM Frequency and Duty Cycle
The PWM signal frequency (f
the counter period and the ATR register value.
Following the above formula, if f
maximum value of f
value = 4094), and the minimum value is 2 kHz
(ATR register value = 0).
Note: The maximum value of ATR is 4094 be-
cause it must be lower than the DCR value which
must be 4095 in this case.
At reset, the counter starts counting from 0.
Software must write the duty cycle value in the
DCR0H and DCR0L preload registers. The
DCR0H register must be written first. See caution
below.
Figure 34. PWM Function
AUTO-RELOAD
DUTY CYCLE
WITH OE0=1
AND OP0=0
WITH OE0=1
AND OP0=1
REGISTER
REGISTER
f
(DCR0)
PWM
(ATR)
= f
4095
000
COUNTER
PWM
is 4 Mhz (ATR register
/ (4096 - ATR)
page
PWM
CPU
58).
) is controlled by
is 8 MHz, the
When a upcounter overflow occurs (OVF event),
the ATR value is loaded in the upcounter, the
preloaded Duty cycle value is transferred to the
Duty Cycle register and the PWM0 signal is set to
a high level. When the upcounter matches the
DCRx value the PWM0 signals is set to a low level.
To obtain a signal on the PWM0 pin, the contents
of the DCR0 register must be greater than the con-
tents of the ATR register.
The polarity bit can be used to invert the output
signal.
The maximum available resolution for the PWM0
duty cycle is:
Note: To get the maximum resolution (1/4096), the
ATR register must be 0. With this maximum reso-
lution and assuming that DCR=ATR, a 0% or
100% duty cycle can be obtained by changing the
polarity .
Caution: As soon as the DCR0H is written, the
compare function is disabled and will start only
when the DCR0L value is written. If the DCR0H
write occurs just before the compare event, the
signal on the PWM output may not be set to a low
level. In this case, the DCRx register should be up-
dated just after an OVF event. If the DCR and ATR
values are close, then the DCRx register shouldbe
updated just before an OVF event, in order not to
miss a compare event and to have the right signal
applied on the PWM output.
Resolution = 1 / (4096 - ATR)
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