Datasheet

110
8246A–AVR–11/09
ATtiny2313A/4313
12.11 Register Description
12.11.1 TCCR1A – Timer/Counter1 Control Register A
• Bit 7:6 – COM1A1:0: Compare Output Mode for Channel A
• Bit 5:4 – COM1B1:0: Compare Output Mode for Channel B
The COM1A1:0 and COM1B1:0 control the Output Compare pins (OC1A and OC1B respec-
tively) 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 Register (DDR) bit correspond-
ing 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 depen-
dent of the WGM13:0 bits setting. Table 12-2 shows the COM1x1:0 bit functionality when the
WGM13:0 bits are set to a Normal or a CTC mode (non-PWM).
Table 12-3 shows the COM1x1:0 bit functionality when the WGM13:0 bits are set to the fast
PWM mode.
Note: 1. A special case occurs when OCR1A/OCR1B equals TOP and COM1A1/COM1B1 is set. In
this case the compare match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 98. for more details.
Bit 7 6 5 4 3210
0x2F (0x4F)
COM1A1 COM1A0 COM1B1 COM1B0 – – WGM11 WGM10 TCCR1A
Read/Write R/W R/W R/W R/W R R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 12-2. Compare Output Mode, non-PWM
COM1A1/COM1B1 COM1A0/COM1B0 Description
00
Normal port operation, OC1A/OC1B
disconnected.
0 1 Toggle OC1A/OC1B on Compare Match.
10
Clear OC1A/OC1B on Compare Match (Set
output to low level).
11
Set OC1A/OC1B on Compare Match (Set output
to high level).
Table 12-3. Compare Output Mode, Fast PWM
(1)
COM1A1/COM1B1 COM1A0/COM1B0 Description
00
Normal port operation, OC1A/OC1B
disconnected.
01
WGM13=0: Normal port operation, OC1A/OC1B
disconnected.
WGM13=1: Toggle OC1A on Compare Match,
OC1B reserved.
10
Clear OC1A/OC1B on Compare Match, set
OC1A/OC1B at TOP
11
Set OC1A/OC1B on Compare Match, clear
OC1A/OC1B at TOP