8-bit AVR Microcontroller

Timer/Counter0 Control Register B

Name:
TCCR0B
Offset:
0x2D
Reset:
0x00
Access:
-
Bit76543210
ICNC0ICES0WGM03WGM02CS0[2:0]
AccessR/WR/WR/WR/WR/WR/WR/W
Reset0000000

Bit 7 – ICNC0: Input Capture Noise Canceler

Input Capture Noise Canceler

Setting this bit (to one) activates the Input Capture Noise Canceler. When the noise canceler is activated, the input from the Input Capture pin (ICP0) is filtered. The filter function requires four successive equal valued samples of the ICP0 pin for changing its output. The Input Capture is therefore delayed by four Oscillator cycles when the noise canceler is enabled.

Bit 6 – ICES0: Input Capture Edge Select

Input Capture Edge Select

This bit selects which edge on the Input Capture pin (ICP0) that is used to trigger a capture event. When the ICES0 bit is written to zero, a falling (negative) edge is used as trigger, and when the ICES0 bit is written to one, a rising (positive) edge will trigger the capture.

When a capture is triggered according to the ICES0 setting, the counter value is copied into the Input Capture Register (ICR0). The event will also set the Input Capture Flag (ICF0), and this can be used to cause an Input Capture Interrupt, if this interrupt is enabled.

When the ICR0 is used as TOP value (see description of the WGM0[3:0] bits located in the TCCR0A and the TCCR0B Register), the ICP0 is disconnected and consequently the Input Capture function is disabled.

Bit 4 – WGM03: Waveform Generation Mode

Waveform Generation Mode

Refer to TCCR0A.

Bit 3 – WGM02: Waveform Generation Mode

Waveform Generation Mode

Refer to TCCR0A.

Bits 2:0 – CS0[2:0]: Clock Select

Clock Select

The three Clock Select bits select the clock source to be used by the Timer/Counter. Refer to Figure 1 and Figure 2.

Table 1. Clock Select Bit Description
CA0[2] CA0[1] CS0[0] Description
0 0 0 No clock source (Timer/Counter stopped).
0 0 1 clkI/O/1 (No prescaling)
0 1 0 clkI/O/8 (From prescaler)
0 1 1 clkI/O/64 (From prescaler)
1 0 0 clkI/O/256 (From prescaler)
1 0 1 clkI/O/1024 (From prescaler)
1 1 0 External clock source on T0 pin. Clock on falling edge.
1 1 1 External clock source on T0 pin. Clock on rising edge.

If external pin modes are used for the Timer/Counter 0, transitions on the T0 pin will clock the counter even if the pin is configured as an output. This feature allows software control of the counting.