ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 117

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

16-bit Timer/Counter
Register Description
Timer/Counter1 Control
Register A – TCCR1A
2570A–AVR–09/04
Figure 52. Timer/Counter Timing Diagram, with Prescaler (f
• Bit 7:6 – COM1A1:0: Compare Output Mode for Unit A
• Bit 5:4 – COM1B1:0: Compare Output Mode for Unit B
The COM1A1:0 and COM1B1:0 control the Output Compare pins (OC1A and OC1B
respectively) behavior. If one or both of the COM1A1:0 bits are written to one, the OC1A
output overrides the normal port functionality of the I/O pin it is connected to. If one or
both of the COM1B1:0 bit are written to one, the OC1B output overrides the normal port
functionality of the I/O pin it is connected to. However, note that the Data Direction Reg-
ister (DDR) bit corresponding to the OC1A or OC1B pin must be set in order to enable
the output driver.
When the OC1A or OC1B is connected to the pin, the function of the COM1x1:0 bits is
dependent of the WGM13:0 bits setting. Table 53 shows the COM1x1:0 bit functionality
when the WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
Table 53. Compare Output Mode, non-PWM
Bit
Read/Write
Initial Value
COM1A1/COM1B1
and ICF n
(PC and PFC PWM)
TOVn
(CTC and FPWM)
(Update at TOP)
OCRnx
TCNTn
TCNTn
as TOP)
(clk
clk
clk
I/O
(FPWM)
I/O
0
0
1
1
Tn
/8)
(if used
COM1A1
R/W
7
0
COM1A0
COM1A0/COM1B0
R/W
6
0
TOP - 1
TOP - 1
Old OCRnx Value
0
1
0
1
COM1B1
R/W
5
0
ATmega325/3250/645/6450
COM1B0
R/W
4
0
Description
Normal port operation, OC1A/OC1B
disconnected.
Toggle OC1A/OC1B on Compare Match.
Clear OC1A/OC1B on Compare Match (Set
output to low level).
Set OC1A/OC1B on Compare Match (Set output
to high level).
TOP
TOP
R
3
–
0
R
BOTTOM
2
–
0
TOP - 1
clk_I/O
New OCRnx Value
WGM11
R/W
/8)
1
0
WGM10
BOTTOM + 1
R/W
TOP - 2
0
0
TCCR1A
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