Clocks; Rtc Functional Description - Microchip Technology megaAVR 0 Series Manual

PIT - Periodic Interrupt Timer
Using the same clock source as the RTC function, the PIT can request an interrupt or trigger an output
event on every nth clock period. n can be selected from {4, 8, 16,.. 32768} for interrupts, and from {64,
128, 256,... 8192} for events.
The PIT uses the same clock source (CLK_RTC) as the RTC function.
21.2.1 Block Diagram
Figure 21-1. Block Diagram
EXTCLK
TOSC1
TOSC2
21.3

Clocks

System clock (CLK_PER) is required to be at least four times faster than RTC clock (CLK_RTC) for
reading counter value, and this is regardless of the RTC_PRESC setting.
A 32.768 kHz crystal can be connected to the TOSC1 or TOSC2 pins, along with any required load
capacitors. An external clock can be used on the TOSC1 pin.
21.4

RTC Functional Description

The RTC peripheral offers two timing functions: the Real-Time Counter (RTC) and a Periodic Interrupt
Timer (PIT). This subsection describes the RTC.
©
2018 Microchip Technology Inc.
External Clock
32.768 kHz Crystal Osc
32.768 kHz Int. Osc
RTC
CLKSEL
Correction
counter
CLK_RTC
15-bit
prescaler
PIT
Period
Datasheet Preliminary
®
megaAVR 0-Series
Real-Time Counter (RTC)
PER
= Overflow
CNT
= Compare
CMP
DS40002015A-page 256