192
XMEGA A [MANUAL]
8077I–AVR–11/2012
17.3.6 CNTL – Counter register Low
The CNTH and CNTL register pair represents the 16-bit value, CNT. CNT counts positive clock edges on the prescaled
RTC clock. Reading and writing 16-bit values requires special attention. Refer to “Accessing 16-bit Registers” on page 12
for details.
Due to synchronization between the RTC clock and system clock domains, there is a latency of two RTC clock cycles
from updating the register until this has an effect. Application software needs to check that the SYNCBUSY flag in the
“STATUS – Status register” on page 190 is cleared before writing to this register.
Bit 7:0
CNT[7:0]: Counter value low byte
These bits hold the LSB of the 16-bit real-time counter value.
17.3.7 CNTH – Counter register High
Bit 7:0 – CNT[15:8]: Counter value high byte
These bits hold the MSB of the 16-bit real-time counter value.
17.3.8 PERL – Period register Low
The PERH and PERL register pair represents the 16-bit value, PER. PER is constantly compared with the counter value
(CNT). A match will set OVFIF in the INTFLAGS register and clear CNT. Reading and writing 16-bit values requires
special attention. Refer to “Accessing 16-bit Registers” on page 12 for details.
Due to synchronization between the RTC clock and system clock domains, there is a latency of two RTC clock cycles
from updating the register until this has an effect. Application software needs to check that the SYNCBUSY flag in the
“STATUS – Status register” on page 190 is cleared before writing to this register.
Bit 7:0 – PER[7:0]: Period Low byte
These bits hold the LSB of the 16-bit RTC TOP value.
17.3.9 PERH – Period register High
Bits 7:0 – PER[15:8]: Period high byte
These bits hold the MSB of the 16-bit RTC TOP value.
Bit
765
43
210
+0x08
CNT[7:0]
Read/Write
R/W
Initial Value
0
Bit
7
65
43
210
+0x09
CNT[15:8]
Read/Write
R/W
Initial Value
0
00
000
Bit
765
43
210
+0x0A
PER[7:0]
Read/Write
R/W
Initial Value
1
Bit
7
65
43
21
0
+0x0B
PER[15:8]
Read/Write
R/W
Initial Value
1
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