118
AT90PWM216/316 [DATASHEET]
7710H–AVR–07/2013
When the ICRn is used as TOP value (see description of the WGMn3:0 bits located in the TCCRnA and the
TCCRnB Register), the ICPn 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 TCCRnB is written.
Bit 4:3 – WGMn3:2: Waveform Generation Mode
See TCCRnA Register description.
Bit 2:0 – CSn2:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see
Figure 14-10 and
FigureIf external pin modes are used for the Timer/Countern, transitions on the Tn pin will clock the counter even if the
pin is configured as an output. This feature allows software control of the counting.
14.10.3
Timer/Counter1 Control Register C – TCCR1C
Bit 7 – FOCnA: Force Output Compare for Channel A
Bit 6 – FOCnB: Force Output Compare for Channel B
The FOCnA/FOCnB bits are only active when the WGMn3:0 bits specifies a non-PWM mode. However, for ensur-
ing compatibility with future devices, these bits must be set to zero when TCCRnA is written when operating in a
PWM mode. When writing a logical one to the FOCnA/FOCnB bit, an immediate compare match is forced on the
Waveform Generation unit. The OCnA/OCnB output is changed according to its COMnx1:0 bits setting. Note that
the FOCnA/FOCnB bits are implemented as strobes. Therefore it is the value present in the COMnx1:0 bits that
determine the effect of the forced compare.
A FOCnA/FOCnB strobe will not generate any interrupt nor will it clear the timer in Clear Timer on Compare match
(CTC) mode using OCRnA as TOP.
The FOCnA/FOCnB bits are always read as zero.
Table 14-5.
Clock Select Bit Description
CSn2
CSn1
CSn0
Description
0
No clock source (Timer/Counter stopped).
001
clk
I/O/1 (No prescaling)
010
clkI/O/8 (From prescaler)
011
clkI/O/64 (From prescaler)
100
clk
I/O/256 (From prescaler)
101
clkI/O/1024 (From prescaler)
1
0
External clock source on Tn pin. Clock on falling edge.
1
External clock source on Tn pin. Clock on rising edge.
Bit
7
65
4
3
210
FOC1A
FOC1B
–
TCCR1C
Read/Write
R/W
R
Initial Value
0