Moteur de recherche de fiches techniques de composants électroniques |
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HT82B40R Fiches technique(PDF) 19 Page - Holtek Semiconductor Inc |
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HT82B40R Fiches technique(HTML) 19 Page - Holtek Semiconductor Inc |
19 / 54 page HT82B40R/HT82B40A Rev. 1.70 19 November 5, 2014 the port control register configures the pin as an input. It should be noted that in the event counting mode, even if the microcontroller is in the Power Down Mode, the Timer/Event Counter will continue to record externally changing logic events on the timer input pin. As a result when the timer overflows it will generate a timer interrupt and corresponding wake-up source. Configuring the Pulse Width Measurement Mode In this mode, the Timer/Event Counter can be utilised to measure the width of external pulses applied to the ex- ternal timer pin. To operate in this mode, the Operating Mode Select bit pair, T0M1/T0M0 or T1M1/T1M0, in the Timer Control Register must be set to the correct valueas shown. Control Register Operating Mode Select Bits for the Pulse Width Measurement Mode Bit7 Bit6 11 In this mode the internal clock, fSYS/4 is used as the in- ternal clock for the Timer/Event Counters. After the other bits in the Timer Control Register have been setup, the enable bit T0ON or T1ON, which is bit 4 of the Timer Control Register, can be set high to enable the Timer/Event Counter, however it will not actually start counting until an active edge is received on the external timer pin. If the Active Edge Select bit T0E or T1E, which is bit 3 of the Timer Control Register, is low, once a high to low transition has been received on the external timer pin, TMR0 or TMR1, the Timer/Event Counter will start counting until the external timer pin returns to its original high level. At this point the enable bit will be automati- cally reset to zero and the Timer/Event Counter will stop counting. If the Active Edge Select bit is high, the Timer/Event Counter will begin counting once a low to high transition has been received on the external timer pin and stop counting when the external timer pin re- turns to its original low level. As before, the enable bit will be automatically reset to zero and the Timer/Event Counter will stop counting. It is important to note that in the Pulse Width Measurement Mode, the enable bit is automatically reset to zero when the external control signal on the external timer pin returns to its original level, whereas in the other two modes the enable bit can only be reset to zero under program control. The residual value in the Timer/Event Counter, which can now be read by the program, therefore represents the length of the pulse received on the external timer pin. As the enable bit has now been reset, any further transitions on the external timer pin will be ignored. Not until the enable bit is again set high by the program can the timer begin further pulse width measurements. In this way, single shot pulse measurements can be easily made. It should be noted that in this mode the Timer/Event Counter is controlled by logical transitions on the exter- nal timer pin and not by the logic level. When the Timer/Event Counter is full and overflows, an interrupt signal is generated and the Timer/Event Counter will re- load the value already loaded into the preload register and continue counting. The interrupt can be disabled by ensuring that the Timer/Event Counter Interrupt Enable bit in the Interrupt Control Register, INTC, is reset to zero. As the external timer pin is shared with an I/O pin, to en- sure that the pin is configured to operate as a pulse width measurement pin, two things have to happen. The first is to ensure that the Operating Mode Select bits in the Timer Control Register place the Timer/Event Coun- ter in the Pulse Width Measurement Mode, the second is to ensure that the port control register configures the pin as an input.ot by the logic level. + 1 + 2 + 3 + 4 T i m e r E x t e r n a l T i m e r P i n I n p u t T 0 O N o r T 1 O N ( w i t h T 0 E o r T 1 E = 0 ) P r e s c a l e r O u t p u t I n c r e m e n t T i m e r C o u n t e r P r e s c a l e r O u t p u t i s s a m p l e d a t e v e r y f a l l i n g e d g e o f T 1 . Pulse Width Measure Mode Timing Chart |
Numéro de pièce similaire - HT82B40R_14 |
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Description similaire - HT82B40R_14 |
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