Figure 12-1. Rtc Block Diagram; Theory Of Operation - Sharp LH79524 User Manual

Chapter 12
Real Time Clock
The Real Time Clock (RTC) can be used as a basic alarm, a long time-base counter, a
time base for a true real-time clock, or as a wake-up interrupt generator to transfer the
LH79524/LH79525 from Standby, Sleep, Stop1, or Stop2 mode to Active mode. The RTC
can be programmed to issue an interrupt when the RTC count matches a programmed
value. Figure 12-1 shows a block diagram of the RTC.
The RTC is identical in both the LH79524 and LH79525; all descriptions in this chapter
apply to both SoCs.

12.1 Theory of Operation

The RTC is based on a free-running 32-bit up-counter, clocked at 1 Hz. The RTC must be
enabled in the Reset, Clock and Power Controller (RCPC) block, programming the
PCKLCTRL0:RTC bit to 1. If the RTC is not used, program the PCKLCTRL0:RTC bit to 0,
and the external 32.768 kHz crystal need not be provided. The XTAL32IN signal floats,
therefore it should be tied LOW. (Clock generation is discussed in greater detail in Chapter
13, Reset, Clock, and Power Controller.)
Following reset, the RTC is disabled (as is the RTC Interrupt). Software must enable the
RTC by programming the CR:START to 1. Once started, the 32-bit counter begins count-
ing from 0x00000001, and upon reaching 0xFFFFFFFF, the counter wraps to 0x00000000
and continues incrementing. It cannot be stopped once it is started.
HCLK
ADVANCED
PERIPHERAL
BUS (APB)
AMBA
APB
INTERFACE

Figure 12-1. RTC Block Diagram

Version 1.0
1 Hz CLOCK
REGISTER CONTROL
BLOCK BLOCK
RTC
INTERRUPT
LH79525-51
12-1