Datasheet

Table Of Contents
21.9.1. TCCR0 – Timer/Counter Control Register
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When
addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset
addresses.
Name:  TCCR0
Offset:  0x25
Reset:  0x00
Property:
 
When addressing I/O Registers as data space the offset address is 0x45
Bit 7 6 5 4 3 2 1 0
FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00
Access
W R/W R/W R/W R/W R/W R/W R/W
Reset 0 0 0 0 0 0 0 0
Bit 7 – FOC0: Force Output Compare
The FOC0 bit is only active when the WGM00 bit specifies a non-PWM mode. However, for ensuring
compatibility with future devices, this bit must be set to zero when TCCR0 is written when operating in
PWM mode. When writing a logical one to the FOC0 bit, an immediate Compare Match is forced on the
waveform generation unit. The OC0 output is changed according to its COM21:0 bits setting. Note that
the FOC0 bit is implemented as a strobe. Therefore it is the value present in the COM01:0 bits that
determines the effect of the forced compare.
A FOC0 strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0 as
TOP.
The FOC0 bit is always read as zero.
Bit 6 – WGM00: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP) counter
value, and what type of waveform generation to be used. Modes of operation supported by the Timer/
Counter unit are: Normal mode, Clear Timer on Compare Match (CTC) mode, and two types of Pulse
Width Modulation (PWM) modes. See table below and Modes of Operation.
Table 21-2. Waveform Generation Mode Bit Description
Mode WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter Mode of Operation
(1)
TOP Update of
OCR0
TOV0 Flag
Set
0 0 0 Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR0 Immediate MAX
3 1 1 Fast PWM 0xFF BOTTOM MAX
Note:  1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 definitions.
However, the functionality and location of these bits are compatible with previous versions of the timer.
Bits 5:4 – COM0n: Compare Match Output Mode [n = 1:0]
These bits control the Output Compare Pin (OC0) behavior. If one or both of the COM01:0 bits are set,
the OC0 output overrides the normal port functionality of the I/O pin it is connected to. However, note that
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