130
ATmega64A [DATASHEET]
8160D–AVR–02/2013
16.11.6
TCCR3C – Timer/Counter3 Control Register C
Bit 7 – FOCnA: Force Output Compare for Channel A
Bit 6 – FOCnB: Force Output Compare for Channel B
Bit 5 – FOCnC: Force Output Compare for Channel C
The FOCnA/FOCnB/FOCnC bits are only active when the WGMn3:0 bits specifies a non-PWM mode. When writ-
ing a logical one to the FOCnA/FOCnB/FOCnC bit, an immediate Compare Match is forced on the waveform
generation unit. The OCnA/OCnB/OCnC output is changed according to its COMnx1:0 bits setting. Note that the
FOCnA/FOCnB/FOCnC 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/FOCnC strobe will not generate any interrupt nor will it clear the timer in Clear Timer on Com-
pare match (CTC) mode using OCRnA as TOP.
The FOCnA/FOCnB/FOCnB bits are always read as zero.
Bit 4:0 – Reserved Bits
These bits are reserved for future use. For ensuring compatibility with future devices, these bits must be written to
zero when TCCRnC is written.
16.11.7
TCNT1H and TCNT1L – Timer/Counter1
16.11.8
TCNT3H and TCNT3L – Timer/Counter3
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.
SeeModifying the counter (TCNTn) while the counter is running introduces a risk of missing a Compare 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
765
43210
FOC3A
FOC3B
FOC3C
–––––
TCCR3C
Read/Write
W
RRRR
R
Initial Value
000
00000
Bit
765
43210
TCNT1[15:8]
TCNT1H
TCNT1[7:0]
TCNT1L
Read/Write
R/W
Initial Value
000
00000
Bit
765
43210
TCNT3[15:8]
TCNT3H
TCNT3[7:0]
TCNT3L
Read/Write
R/W
Initial Value
000
00000