Atmel Xplained Pro Evaluation Kit for the ATSAMD21J18A Microcontroller ATSAMD21-XPRO ATSAMD21-XPRO Data Sheet
Product codes
ATSAMD21-XPRO
601
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181C–SAM-D21_Datasheet–07/2014
29.5.8 Register Access Protection
All registers with write-access are optionally write-protected by the peripheral access controller (PAC), except the
following registers:
following registers:
z
Interrupt Flag register (
)
z
)
z
z
z
Period register (PER),
z
Compare/Capture Value registers (CCx),
Write-protection is denoted by the Write-Protection property in the register description.
When the CPU is halted in debug mode, all write-protection is automatically disabled.
Write-protection does not apply for accesses through an external debugger. Refer to
29.5.9 Analog Connections
Not applicable.
29.6 Functional Description
29.6.1 Principle of Operation
The counter in the TC can be set to count on events from the Event System, or on the GCLK_TCx frequency. The pulses
from GCLK_TCx will go through the prescaler, where it is possible to divide the frequency down.
from GCLK_TCx will go through the prescaler, where it is possible to divide the frequency down.
The value in the counter is passed to the compare/capture channels, where it can either be compared with user defined
values or captured on a predefined event.
values or captured on a predefined event.
The TC can be configured as an 8-, 16- or 32-bit counter. Which mode is chosen will determine the maximum range of
the counter. The counter range combined with the operating frequency will determine the maximum time resolution
achievable with the TC peripheral.
the counter. The counter range combined with the operating frequency will determine the maximum time resolution
achievable with the TC peripheral.
The TC can be count up or down. By default, the counter will operate in a continuous mode and count up, where the
counter will wrap to the zero when reaching the top value
counter will wrap to the zero when reaching the top value
When one of the compare/capture channels is used in compare mode, the TC can be used for waveform generation.
Upon a match between the counter and the value in one or more of the Compare/Capture Value registers (CCx), one or
more output pins on the device can be set to toggle. The CCx registers and the counter can thereby be used in frequency
generation and PWM generation.
Upon a match between the counter and the value in one or more of the Compare/Capture Value registers (CCx), one or
more output pins on the device can be set to toggle. The CCx registers and the counter can thereby be used in frequency
generation and PWM generation.
Capture mode can be used to automatically capture the period and pulse width of signals.
29.6.2 Basic Operation
29.6.2.1 Initialization
The following register is enable-protected, meaning that it can only be written when the TC is disabled (CTRLA.ENABLE
is zero):
is zero):
z
), except the Run Standby (RUNSTDBY), Enable (ENABLE) and Software Reset
(SWRST) bits
The following bits are enable-protected:
z
Event Action bits in the Event Control register (EVCTRL.EVACT)
Enable-protected bits in the CTRLA register can be written at the same time as CTRLA.ENABLE is written to one, but not
at the same time as CTRLA.ENABLE is written to zero.
at the same time as CTRLA.ENABLE is written to zero.
Before the TC is enabled, it must be configured, as outlined by the following steps: