8 REAL-TIME CLOCK (RTC)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
8-1
Real-Time Clock (RTC)
8
RTC Module Overview
8.1
The S1C33L26 incorporates a real-time clock (RTC) with a perpetual calendar, and an OSC1 oscillator circuit to
generate the operating clock for the RTC.
The RTC and OSC1 oscillator circuit operate in SLEEP mode. Moreover, the RTC can periodically generate inter-
rupt requests to the CPU.
The main features of the RTC are outlined below.
• Contains time counters (seconds, minutes, and hours) and calendar counters (days, days of the week, months, and
year).
• BCD data can be read from and written to both counters.
• Includes read buffers to prevent carry over at reading.
• Capable of controlling the starting and stopping of time clocks.
• 24-hour or 12-hour mode can be selected.
• A 30-second correction function can be implemented in software.
• Periodic interrupts are possible.
• Interrupt period can be selected from 1/512 second, 1/256 second, 1/128 second, 1/64 second, 1 second, 1 min-
ute, or 1 hour. (Level interrupt mode)
• Independent power supply, so that the RTC can continue operating even when system power is turned off.
• A built-in OSC1 oscillator circuit (crystal oscillator or external clock input) that generates a 32.768-kHz (typ.)
operating clock. (See the “Clock Management Unit (CMU)” chapter.)
• Provides the #STBY and WAKEUP pins to control the system power supply.
Figure 8.1.1 shows a block diagram of the RTC.
1 Hz
24H/12H
1/512–1/64
second
1 second
1 minute
1 hour
CMU
Interrupt request to ITC
(SLEEP release request to CMU)
RTC
OSC1 oscillator
(32 kHz)
Interrupt
control
1-second counter
Read buffer
Divider
Controller
10-second counter
RTCCLKI
RTCCLKO
Standby/
wakeup
control
WAKEUP
#STBY
1-minute counter
10-minute counter
1-hour counter
10-hour counter
AM/PM
1-day counter
10-day counter
1-month counter
10-month counter
1-year counter
10-year counter
Days of week counter
Data bus
1.1 RTC Block Diagram
Figure 8.