st52t430 STMicroelectronics, st52t430 Datasheet - Page 53

• Manufacturer Part Number: st52t430
• Description: 8-bit Intelligent Controller Unit Icu Three Timer/pwms, Adc, Sci
• Manufacturer: STMicroelectronics

The Output Register PWM_x_RELOAD value is
automatically reloaded when Counter x restarts
counting.
The 16-bit Prescaler x divides the master clock,
CLKM, or, only for TIMER0, the external T0CLK
signal, by the 16-bit Prescaler x.
NOTE: The external clock signal, applied on
T0CLK pin must have a frequency at least two
times smaller than the internal master clock.
The Prescaler x output can be selected by setting
PRESCx bit of REG_CONF6, REG_CONF9 and
REG_CONF11 registers (see Table 10.2, Table
10.5 and Table 10.7).
When Counter x reaches the Peripheral Register
PWM_x_COUNT
TIMERxOUT signal changes from high to low level,
up to the next counter start.
The period of the PWM signal is obtained by using
the following equation:
T = (255 - PWM _x_RELOAD)x TMR CLKx
where TMRCLKx is the output of the 16-bit
prescaler x.
The duty cycle of the PWM signal is controlled by
the Output Register PWM_x_COUNT:
Ton =(PWM_x_COUNT- PWM_x_RELOAD)*
If the Output Register PWM_x_COUNT value is
255 the TIMERxOUT signal is always at a high
level.
If the Output Register PWM_x_COUNT is 0, or
less
TIMERxOUT signal is always at a low level.
NOTE. If PWM_x_RELOAD value increases the
duty cycle resolution decreases.
By using a 20 MHz clock master a PWM frequency
in the range 1.2 Hz to 78.43 Khz can be obtained.
NOTE: loading new values of the counter in the
PWM_x_COUNT register, in order to avoid side
effects, the PWM/Timer counter is updated only
at the end of the counting cycle.
TMRCLKx
than
the
value
PWM_x_RELOAD
(Compare
Value),
value,
WARNING: loading new values of the reload in
the PWM_x_RELOAD registers, the PWM/Timer
is immediately set on-fly. This can cause some
side effects during the current counting cycle.
The next cycles work normally. This occurs
both in Timer and in PWM mode.
When the Timers are in Reset, or when the
device is reset, TxOut pins go in threestate. If
these outputs are used to drive external
devices it is recommended to put a pull-up or a
pull-down resistor.
10.3 Timer Interrupt
TIMERx can be programmed to generate an
Interrupt request until the end of the count or when
there is an external TSTART signal. The Timer can
generate programmable Interrupts into 4 different
modes:
Interrupt mode 1: Interrupt on counter Stop.
Interrupt mode 2: Interrupt on Rising Edge of
TIMEROUT.
Interrupt mode 3: Interrupt on Falling Edge of
TIMEROUT.
Interrupt mode 4: Interrupt on both edges of
TIMEROUT.
Interrupt mode can be selected by means of
INTSLx and INTEx bits of the REG_CONF5,
REG_CONF8 and REG_CONF10 registers (see
Table 10.1, Table 10.4 and Table 10.6).
NOTE: the interrupt on TIMEROUT rising edge
is also generated after the Start.
WARNING: the first interrupt after starting
PWM is not generated if the counter value is 0,
255, or lower than the reload value. If the PWM/
Timer is configured with the Interrupt on Stop
and the Start/Stop is configured as external, a
low signal in the STRT pin determines a PWM/
Timer interrupt even if the peripheral is off. If
the interrupt is configured on falling edge, a
reset signal generates an interrupt request.
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