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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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ATmega16-16PU Datenblatt(PDF) 95 Page - ATMEL Corporation |
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ATmega16-16PU Datenblatt(HTML) 95 Page - ATMEL Corporation |
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95 / 357 page  95 2466S–AVR–05/09 ATmega16(L) Counter Unit The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 41 shows a block diagram of the counter and its surroundings. Figure 41. Counter Unit Block Diagram Signal description (internal signals): Count Increment or decrement TCNT1 by 1. Direction Select between increment and decrement. Clear Clear TCNT1 (set all bits to zero). clk T1 Timer/Counter clock. TOP Signalize that TCNT1 has reached maximum value. BOTTOM Signalize that TCNT1 has reached minimum value (zero). The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT1H) con- taining the upper eight bits of the counter, and Counter Low (TCNT1L) containing the lower 8 bits. The TCNT1H Register can only be indirectly accessed by the CPU. When the CPU does an access to the TCNT1H I/O location, the CPU accesses the High byte temporary register (TEMP). The temporary register is updated with the TCNT1H value when the TCNT1L is read, and TCNT1H is updated with the temporary register value when TCNT1L is written. This allows the CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNT1 Register when the counter is counting that will give unpredictable results. The special cases are described in the sections where they are of importance. Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk T1). The clkT1 can be generated from an external or internal clock source, selected by the Clock Select bits (CS12:0). When no clock source is selected (CS12:0 = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU, independent of whether clk T1 is present or not. A CPU write overrides (has priority over) all counter clear or count operations. The counting sequence is determined by the setting of the Waveform Generation Mode bits (WGM13:0) located in the Timer/Counter Control Registers A and B (TCCR1A and TCCR1B). There are close connections between how the counter behaves (counts) and how waveforms are generated on the Output Compare outputs OC1x. For more details about advanced counting sequences and waveform generation, see “Modes of Operation” on page 101. The Timer/Counter Overflow (TOV1) Flag is set according to the mode of operation selected by the WGM13:0 bits. TOV1 can be used for generating a CPU interrupt. TEMP (8-bit) DATA BUS (8-bit) TCNTn (16-bit Counter) TCNTnH (8-bit) TCNTnL (8-bit) Control Logic Count Clear Direction TOVn (Int.Req.) Clock Select TOP BOTTOM Tn Edge Detector ( From Prescaler ) clk Tn |
Ähnliche Teilenummer - ATmega16-16PU |
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Ähnliche Beschreibung - ATmega16-16PU |
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