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HT82R732 Datasheet(PDF) 35 Page - Holtek Semiconductor Inc |
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HT82R732 Datasheet(HTML) 35 Page - Holtek Semiconductor Inc |
35 / 74 page Timer/Event Counters The provision of timers form an important part of any microcontroller, giving the designer a means of carrying out time related functions. The device contains two count-up timers of 8-bit capacity. As the timers have three different operating modes, they can be configured to operate as a general timer, an external event counter or as a pulse width capture device. The provision of an internal prescaler to the clock circuitry on gives added range to the timers. There are two types of registers related to the Timer/Event Counters. The first is the register that contains the actual value of the timer and into which an initial value can be preloaded. Reading from this register retrieves the contents of the Timer/Event Counter. The second type of associated register is the Timer Control Register which defines the timer options and determines how the timer is to be used. The device can have the timer clock configured to come from the internal clock source. In addition, the timer clock source can also be configured to come from an external timer pin. Configuring the Timer/Event Counter Input Clock Source The Timer/Event Counter clock source can originate from various sources, an internal clock or an external pin. The internal clock source is used when the timer is in the timer mode or in the pulse width capture mode. For Timer/Event Counter 0, this internal clock source is first divided by a prescaler, the division ratio of which is conditioned by the Timer Control Register bits T0PSC0~T0PSC2. For Timer/Event Counter 0, the internal clock source can be either fSYS or the LXT Oscillator, the choice of which is determined by the T0S bit in the TMR0C register. An external clock source is used when the Timer/Event Counter n is in the event counting mode, the clock source being provided on an external timer pin TCn. Depending upon the condition of the TnE bit, each high to low, or low to high transition on the external timer pin will increment the counter by one. Timer Registers - TMR0, TMR1 The timer registers are special function registers located in the Special Purpose Data Memory and is the place where the actual timer value is stored. These registers are known as TMR0 and TMR1. The value in the timer registers increases by one each time an internal clock pulse is received or an external transition occurs on the external timer pin. The timer will count from the initial value loaded by the preload register to the full count of FFH at which point the timer overflows and an internal interrupt signal is generated. The timer value will then be reset with the initial preload register value and continue counting. Note that to achieve a maximum full range count of FFH, the preload register must first be cleared to all zeros. It should be noted that after power-on, the preload registers will be in an unknown condition. Note that if the Timer/Event Counter is in an OFF condition and data is written to its preload register, this data will be immediately written into the actual counter. However, if the counter is enabled and counting, any new data written into the preload data register during this period will remain in the preload register and will only be written into the actual counter the next time an overflow occurs. HT82R732 e-Banking 8-Bit OTP MCU Rev. 1.00 35 October 31, 2013 |
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