Datenblatt-Suchmaschine für elektronische Bauteile |
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HT82R732 Datenblatt(PDF) 41 Page - Holtek Semiconductor Inc |
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HT82R732 Datenblatt(HTML) 41 Page - Holtek Semiconductor Inc |
41 / 74 page PFD will not function. The bit PB4 or PA3 must be set high to activate the PFD. These output data bits can be used as the on/off control bit for the PFD outputs. Note that the PFD outputs will all be low if the output data bit is cleared to zero. Using this method of frequency generation, and if a crystal oscillator is used for the system clock, very precise values of frequency can be generated. Note: The PFD is pin-shared with PA3 as well. If this PA3 pn-shared functon is selected, the designer should refer the PB4 settings for PA3. 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 initialized 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 initialized the timer can be turned on and off by controlling the enable bit in the timer control register. HT82R732 e-Banking 8-Bit OTP MCU Rev. 1.00 41 October 31, 2013 T i m e r O v e r f l o w P F D C l o c k P B 4 D a t a P F D O u t p u t a t P B 4 PFD Function |
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