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ATmega16-16PU 数据表(PDF) 72 Page - ATMEL Corporation |
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ATmega16-16PU 数据表(HTML) 72 Page - ATMEL Corporation |
72 / 357 page 72 2466S–AVR–05/09 ATmega16(L) Unit” on page 73. for details. The compare match event will also set the Compare Flag (OCF0) which can be used to generate an output compare interrupt request. Definitions Many register and bit references in this document are written in general form. A lower case “n” replaces the Timer/Counter number, in this case 0. However, when using the register or bit defines in a program, the precise form must be used i.e., TCNT0 for accessing Timer/Counter0 counter value and so on. The definitions in Table 37 are also used extensively throughout the document. Timer/Counter Clock Sources The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the clock select logic which is controlled by the clock select (CS02:0) bits located in the Timer/Counter Control Register (TCCR0). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 87. Counter Unit The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure 28 shows a block diagram of the counter and its surroundings. Figure 28. Counter Unit Block Diagram Signal description (internal signals): count Increment or decrement TCNT0 by 1. direction Select between increment and decrement. clear Clear TCNT0 (set all bits to zero). clk Tn Timer/Counter clock, referred to as clk T0 in the following. TOP Signalize that TCNT0 has reached maximum value. BOTTOM Signalize that TCNT0 has reached minimum value (zero). Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk T0). clkT0 can be generated from an external or internal clock source, selected by the Clock Select bits (CS02:0). When no clock source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of Table 37. Definitions BOTTOM The counter reaches the BOTTOM when it becomes 0x00. MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255). TOP The counter reaches the TOP when it becomes equal to the highest value in the count sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR0 Register. The assignment is dependent on the mode of operation. DATA BUS TCNTn Control Logic count TOVn (Int. Req.) Clock Select TOP Tn Edge Detector ( From Prescaler ) clk Tn BOTTOM direction clear |
类似零件编号 - ATmega16-16PU |
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类似说明 - ATmega16-16PU |
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