Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
135
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
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.
pin is configured as an output. This feature allows software control of the counting.
16.11.3 TCCR1C – Timer/Counter1 Control Register C
• Bit 7 – FOC1A: Force Output Compare for Channel A
• Bit 6 – FOC1B: Force Output Compare for Channel B
The FOC1A/FOC1B bits are only active when the WGM13:0 bits specifies a non-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.
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.
match (CTC) mode using OCR1A as TOP. The FOC1A/FOC1B bits are always read as zero.
16.11.4 TCNT1H and TCNT1L – Timer/Counter1
The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) 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. See
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. See
.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a compare match
between TCNT1 and one of the OCR1x Registers.
between TCNT1 and one of the OCR1x Registers.
Writing to the TCNT1 Register blocks (removes) the compare match on the following timer clock for all compare
units.
units.
Table 16-5.
Clock Select Bit Description
CS12
CS11
CS10
Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clk
I/O
/1 (No prescaling)
0
1
0
clk
I/O
/8 (From prescaler)
0
1
1
clk
I/O
/64 (From prescaler)
1
0
0
clk
I/O
/256 (From prescaler)
1
0
1
clk
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
7
6
5
4
3
2
1
0
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
Bit
7
6
5
4
3
2
1
0
TCNT1[15:8]
TCNT1H
TCNT1[7:0]
TCNT1L
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0