ATMEGA128-16AU SL383 Atmel, ATMEGA128-16AU SL383 Datasheet - Page 138

• Manufacturer Part Number: ATMEGA128-16AU SL383
• Manufacturer: Atmel

Timer/Counter1 –
TCNT1H and TCNT1L
Timer/Counter3 –
TCNT3H and TCNT3L
Output Compare
Register 1 A –
OCR1AH and OCR1AL
Output Compare
Register 1 B –
OCR1BH and OCR1BL
Output Compare
Register 1 C –
OCR1CH and OCR1CL
Output Compare
Register 3 A –
OCR3AH and OCR3AL
138
ATmega128
The two Timer/Counter I/O locations (TCNTnH and TCNTnL, combined TCNTn) 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.
bit Registers” on page 115.
Modifying the counter (TCNTn) while the counter is running introduces a risk of missing a com-
pare match between TCNTn and one of the OCRnx Registers.
Writing to the TCNTn Register blocks (removes) the compare match on the following timer clock
for all compare units.
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
R/W
R/W
R/W
R/W
R/W
R/W
7
0
7
0
7
0
7
0
7
0
7
0
R/W
R/W
R/W
R/W
R/W
R/W
6
0
6
0
6
0
6
0
6
0
6
0
R/W
R/W
R/W
R/W
R/W
R/W
5
0
5
0
5
0
5
0
5
0
5
0
R/W
R/W
R/W
R/W
R/W
R/W
OCR1A[15:8]
OCR1B[15:8]
OCR1C[15:8]
OCR3A[15:8]
TCNT1[15:8]
TCNT3[15:8]
4
0
4
0
4
OCR1A[7:0]
0
4
OCR1B[7:0]
0
4
OCR1C[7:0]
0
4
OCR3A[7:0]
0
TCNT1[7:0]
TCNT3[7:0]
R/W
R/W
R/W
R/W
R/W
R/W
3
0
3
0
3
0
3
0
3
0
3
0
R/W
R/W
R/W
R/W
R/W
R/W
2
0
2
0
2
0
2
0
2
0
2
0
R/W
R/W
R/W
R/W
R/W
R/W
1
0
1
0
1
0
1
0
1
0
1
0
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
0
0
0
0
See “Accessing 16-
OCR1AH
OCR1BH
OCR1CH
OCR3AH
OCR1AL
OCR1BL
OCR1CL
OCR3AL
TCNT1H
TCNT1L
TCNT3H
TCNT3L
2467S–AVR–07/09