
C165UTAH
Real Time Clock (RTC)
Data Sheet
290
2001-02-23
13
Real Time Clock (RTC)
13.1
Introduction
The Real Time Clock (RTC) module of the C165UTAH basically is an independent timer
chain and counts time ticks. The base frequency of the RTC can be programmed via a
reload counter. The RTC can work fully asynchronous to the system frequency and is
optimized on low power consumption.
13.1.1
Features
The RTC serves for different purposes:
– System clock to determine the current time and date
– Cyclic time based interrupt
– Alarm interrupt for wake up on a defined time
– 48-bit timer for long term measurements
13.1.2
Overview
The real time clock module provides three different types of registers: two control
registers for controlling the RTC′s functionality, three data registers for setting the clock
divider for RTC base frequency programming and for flexible interrupt generation, and
three counter registers they contain the actual time and date. The interrupts are
programmed via one interrupt sub node register.
13.2
Function Description
The RTC module consists of a chain of 2 divider blocks, the reloadable 16-bit timer T14
and the 32-bit RTC timer (accessible via registers RTCH and RTCL). Both timers count
up. Timer T14 is reloaded with the value of register T14REL on every timer T14
overflow.
The count input of the RTC module (RTC_REF_CLK) can be optional divided by a
prescaler with factor 8, see
Figure 94
.
The RTC module operates in two different modes, an asynchronous and a synchronous
mode. In synchronous mode the RTC module is clocked with a synchronous clock
referring to the CPU clock (RTC clock). In asynchronous mode the RTC module is
clocked with the asynchronous counting input clock (RTC_REF_CLK). The
asynchronous mode is necessary in case of a very low or disabled CPU clock (eg. sleep
mode).
The mode control (asynchronous / synchronous) of the RTC is described as follows:
The RTC is switched to asynchronous mode if SYSCON2.RCS = '1'
The RTC is switched to asynchronous mode if device is in sleep mode.