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ATMEGA649 Datasheet(PDF) 130 Page - ATMEL Corporation |
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ATMEGA649 Datasheet(HTML) 130 Page - ATMEL Corporation |
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130 / 375 page  130 ATmega329/3290/649/6490 2552H–AVR–11/06 TCNT1H and TCNT1L – Timer/Counter1 The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To ensure that both the high and low bytes are read and written simultaneously when the CPU accesses these registers, the access is performed using an 8-bit tempo- rary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 108. Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match between TCNT1 and one of the OCR1x Registers. Writing to the TCNT1 Register blocks (removes) the compare match on the following timer clock for all compare units. OCR1AH and OCR1AL – Output Compare Register 1 A OCR1BH and OCR1BL – Output Compare Register 1 B The Output Compare Registers contain a 16-bit value that is continuously compared with the counter value (TCNT1). A match can be used to generate an Output Compare interrupt, or to generate a waveform output on the OC1x pin. The Output Compare Registers are 16-bit in size. To ensure that both the high and low bytes are written simultaneously when the CPU writes to these registers, the access is performed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 108. ICR1H and ICR1L – Input Capture Register 1 The Input Capture is updated with the counter (TCNT1) value each time an event occurs on the ICP1 pin (or optionally on the Analog Comparator output for Timer/Counter1). The Input Capture can be used for defining the counter TOP value. The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes are read simultaneously when the CPU accesses these registers, the access is per- formed using an 8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit Registers” on page 108. Bit 7654 321 0 (0x85) TCNT1[15:8] TCNT1H (0x84) TCNT1[7:0] TCNT1L Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0000 000 0 Bit 7654 321 0 (0x89) OCR1A[15:8] OCR1AH (0x88) OCR1A[7:0] OCR1AL Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0000 000 0 Bit 7654 321 0 (0x8B) OCR1B[15:8] OCR1BH (0x8A) OCR1B[7:0] OCR1BL Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0000 000 0 Bit 7654 321 0 (0x87) ICR1[15:8] ICR1H (0x86) ICR1[7:0] ICR1L Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 0000 000 0 |
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