HT48R068B Datasheet, PDF (59/121 Pages) Holtek Semiconductor Inc – Enhanced I/O Type 8-bit OTP MCU

HT48R068B/HT48R069B
Enhanced I/O Type 8-bit OTP MCU
T im e r O v e r flo w
P F D C lo c k
P A 1 D a ta
P F D O u tp u t a t P A 1
PFD Function
I/O Interfacing
The Timer/Event Counter, when configured to run in the event counter or pulse width capture
mode, requires the use of an external timer pin for its operation. As this pin is a shared pin it must
be configured correctly to ensure that it is setup for use as a Timer/Event Counter input pin. This is
achieved by ensuring that the mode select bits in the Timer/Event Counter control register, select
either the event counter or pulse width capture mode. Additionally the corresponding Port Control
Register bit must be set high to ensure that the pin is setup as an input. Any pull-high resistor
connected to this pin will remain valid even if the pin is used as a Timer/Event Counter input.
Programming Considerations
When configured to run in the timer mode, the internal system clock is used as the timer clock source
and is therefore synchronised with the overall operation of the microcontroller. In this mode when the
appropriate timer register is full, the microcontroller will generate an internal interrupt signal directing
the program flow to the respective internal interrupt vector. For the pulse width capture mode, the
internal system clock is also used as the timer clock source but the timer will only run when the
correct logic condition appears on the external timer input pin. As this is an external event and not
synchronised with the internal timer clock, the microcontroller will only see this external event when
the next timer clock pulse arrives. As a result, there may be small differences in measured values
requiring programmers to take this into account during programming. The same applies if the timer is
configured to be in the event counting mode, which again is an external event and not synchronised
with the internal system or timer clock.
When the Timer/Event Counter is read, or if data is written to the preload register, the clock is
inhibited to avoid errors, however as this may result in a counting error, this should be taken into
account by the programmer. Care must be taken to ensure that the timers are properly initialised
before using them for the first time. The associated timer enable bits in the interrupt control register
must be properly set otherwise the internal interrupt associated with the timer will remain inactive.
The edge select, timer mode and clock source control bits in timer control register must also be
correctly set to ensure the timer is properly configured for the required application. It is also important
to ensure that an initial value is first loaded into the timer registers before the timer is switched on;
this is because after power-on the initial values of the timer registers are unknown. After the timer has
been initialised the timer can be turned on and off by controlling the enable bit in the timer control
register.
When the Timer/Event Counter overflows, its corresponding interrupt request flag in the interrupt
control register will be set. If the Timer/Event Counter interrupt is enabled this will in turn generate
an interrupt signal. However irrespective of whether the interrupts are enabled or not, a Timer/
Event Counter overflow will also generate a wake-up signal if the device is in a Power-down
condition. This situation may occur if the Timer/Event Counter is in the Event Counting Mode
Rev 1.00
54
February 14, 2011