Datasheet

129
ATmega329/3290/649/6490
2552I–AVR–04/07
(ICF1), and this can be used to cause an Input Capture Interrupt, if this interrupt is
enabled.
When the ICR1 is used as TOP value (see description of the WGM13:0 bits located in
the TCCR1A and the TCCR1B Register), the ICP1 is disconnected and consequently
the Input Capture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit
must be written to zero when TCCR1B is written.
• Bit 4:3 – WGM13:2: Waveform Generation Mode
See TCCR1A Register description.
• Bit 2:0 – CS12:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see
Figure 50 and Figure 51.
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will
clock the counter even if the pin is configured as an output. This feature allows software
control of the counting.
TCCR1C – Timer/Counter1
Control Register C
• Bit 7 – FOC1A: Force Output Compare for Unit A
• Bit 6 – FOC1B: Force Output Compare for Unit B
The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-PWM
mode. However, for ensuring compatibility with future devices, these bits must be set to
zero when TCCR1A is written when operating in a PWM mode. When writing a logical
one to the FOC1A/FOC1B bit, an immediate compare match is forced on the Waveform
Generation unit. The OC1A/OC1B output is changed according to its COM1x1:0 bits
setting. Note that the FOC1A/FOC1B bits are implemented as strobes. Therefore it is
the value present in the COM1x1:0 bits that determine the effect of the forced compare.
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.
Table 65. Clock Select Bit Description
CS12 CS11 CS10 Description
0 0 0 No clock source (Timer/Counter stopped).
001clk
I/O
/1 (No prescaling)
010clk
I/O
/8 (From prescaler)
011clk
I/O
/64 (From prescaler)
100clk
I/O
/256 (From prescaler)
101clk
I/O
/1024 (From prescaler)
1 1 0 External clock source on T1 pin. Clock on falling edge.
1 1 1 External clock source on T1 pin. Clock on rising edge.
Bit 7654 3210
(0x82) FOC1A FOC1B
– – – – – – TCCR1C
Read/Write R/W R/W R R R R R R
Initial Value 0 0 0 0 0 0 0 0