atmega3250v-8auatmega325v-8ai ATMEL Corporation, atmega3250v-8auatmega325v-8ai Datasheet - Page 126

• Manufacturer Part Number: atmega3250v-8auatmega325v-8ai
• Description: Atmega3250 8-bit Microcontroller With In-system Programmable Flash
• Manufacturer: ATMEL Corporation

17.11.4
17.11.5
17.11.6
17.11.7
126
ATmega325/3250/645/6450
TCNT1H and TCNT1L – Timer/Counter1
OCR1AH and OCR1AL – Output Compare Register 1 A
OCR1BH and OCR1BL – Output Compare Register 1 B
ICR1H and ICR1L – Input Capture Register 1
A FOC1A/FOC1B strobe will not generate any interrupt nor will it clear the timer in Clear Timer
on Compare match (CTC) mode using OCR1A as TOP. The FOC1A/FOC1B bits are always
read as zero.
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.
Registers” on page 103.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a com-
pare 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.
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.
Bit
(0x85)
(0x84)
Read/Write
Initial Value
Bit
(0x89)
(0x88)
Read/Write
Initial Value
Bit
(0x8B)
(0x8A)
Read/Write
Initial Value
Bit
(0x87)
(0x86)
Read/Write
Initial Value
R/W
R/W
R/W
R/W
7
0
7
0
7
0
7
0
See “Accessing 16-bit Registers” on page 103.
R/W
R/W
R/W
R/W
6
0
6
0
6
0
6
0
R/W
R/W
R/W
R/W
5
0
5
0
5
0
5
0
R/W
R/W
R/W
R/W
OCR1A[15:8]
OCR1B[15:8]
TCNT1[15:8]
4
0
4
OCR1A[7:0]
0
4
OCR1B[7:0]
0
4
0
TCNT1[7:0]
ICR1[15:8]
ICR1[7:0]
R/W
R/W
R/W
R/W
3
0
3
0
3
0
3
0
R/W
R/W
R/W
R/W
2
0
2
0
2
0
2
0
R/W
R/W
R/W
R/W
1
0
1
0
1
0
1
0
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
See “Accessing 16-bit
OCR1AH
OCR1BH
OCR1AL
OCR1BL
TCNT1H
TCNT1L
ICR1H
ICR1L
2570L–AVR–08/07