Atmel XMEGA B, User Manual

Page: 206 / 415

206 XMEGA B [DATASHEET]
8291B–AVR–01/2013
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 13 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 203 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.
17.3.10 COMPL – Compare register Low
The COMPH and COMPL register pair represent the 16-bit value, COMP. COMP is constantly compared with the
counter value (CNT). A compare match will set COMPIF in the INTFLAGS register. Reading and writing 16-bit values
requires special attention. Refer
“Accessing 16-bit Registers” on page 13 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 203 is cleared before writing to this register.
If the COMP value is higher than the PER value, no RTC compare match interrupt requests or events will ever be
generated.

Bit 7:0 – COMP[7:0]: Compare value low byte
These bits hold the LSB of the 16-bit RTC compare value.
Bit 7 6 5 4 3 2 1 0
+0x0A
PER[7:0]
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 1 1 1 1 1 1 1 1
Bit 7 6 5 4 3 2 1 0
+0x0B
PER[15:8]
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 1 1 1 1 1 1 1 1
Bit 7 6 5 4 3 2 1 0
+0x0C
COMP[7:0]
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