AM1802 Datasheet, PDF (159/180 Pages) Texas Instruments – AM1802 ARM Microprocessor

AM1802
www.ti.com
SPRS710C – NOVEMBER 2010 – REVISED MARCH 2012
5.22.1 Clock Source
The clock reference for the RTC is an external 32.768-kHz crystal or an external clock source of the same
frequency. The RTC also has a separate power supply that is isolated from the rest of the system. When
the CPU and other peripherals are without power, the RTC can remain powered to preserve the current
time and calendar information. Even if the RTC is not used, it must remain powered when the rest of the
device is powered.
The source for the RTC reference clock may be provided by a crystal or by an external clock source. The
RTC has an internal oscillator buffer to support direct operation with a crystal. The crystal is connected
between pins RTC_XI and RTC_XO. RTC_XI is the input to the on-chip oscillator and RTC_XO is the
output from the oscillator back to the crystal.
An external 32.768-kHz clock source may be used instead of a crystal. In such a case, the clock source is
connected to RTC_XI, and RTC_XO is left unconnected.
If the RTC is not used, the RTC_XI pin should be held either low or high, RTC_XO should be left
unconnected, RTC_CVDD should be connected to the device CVDD and RTC_VSS should remain
grounded.
RTC
Power
Source
C2
CV_DD
RTC_CV_DD
RTC_XI
XTAL
32.768
kHz
C1
RTC_XO
32K
OSC
Real
Time
Clock
(RTC)
Module
RTC_VSS
Isolated RTC
Power Domain
Figure 5-52. Clock Source
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Peripheral Information and Electrical Specifications 159
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