Datasheet

 2018 Microchip Technology Inc. Data Sheet Complete DS40002059A-page 47
ATxmega32E5/16E5/8E5
Figure 21-1. Real-time Counter Overview
The RTC also supports correction when operated using external 32.768 kHz crystal oscillator. An externally calibrated
value will be used for correction. The calibration can be done by measuring the default RTC frequency relative to a more
accurate clock input to the device as system clock. The RTC can be calibrated to an accuracy of ±0.5ppm. The RTC cor-
rection operation will either speed up (by skipping count) or slow down (adding extra cycles) the prescaler to account for
the crystal oscillator error.
32.768 kHz Crystal
Osc
32.768 kHz Int. Osc
TOSC1
TOSC2
External Clock
DIV32
32 kHz int ULP
(DIV32)
RTCSRC
clk
RTC
CNT
PER
COMP
=
=
”match”/
Compare
TOP/
Overflow
CALIB
Correction
Counter
Hold Count
DIV32
10-bit
prescaler