Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 140
16.12.4 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 temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit
registers. See “Accessing 16-bit Registers” on page 117.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match
between TCNT1 and one of the OCRnx Registers.
Writing to the TCNT1 Register blocks (removes) the compare match on the following timer clock for all compare
units.
16.12.5 TCNT3H and TCNT3L –Timer/Counter3
The two Timer/Counter I/O locations (TCNT3H and TCNT3L, combined TCNT3) 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 temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit
registers. See “Accessing 16-bit Registers” on page 117.
Modifying the counter (TCNT3) while the counter is running introduces a risk of missing a compare match
between TCNT3 and one of the OCRnx Registers.
Writing to the TCNT3 Register blocks (removes) the compare match on the following timer clock for all compare
units.
16.12.6 OCR1AH and OCR1AL – Output Compare Register1 A
16.12.7 OCR1BH and OCR1BL – Output Compare Register1 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 OCnx pin.
Bit 76543210
(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 Value00000000
Bit 76543210
(0x95) TCNT3[15:8] TCNT3H
(0x94) TCNT3[7:0] TCNT3L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
(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 Value00000000
Bit 76543210
(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 Value00000000