Interrupts; Usage Notes; Register Initialization; Carry Flag And Interrupt Flag In Standby Mode - Hitachi SH7751 Hardware Manual

11.4

Interrupts

There are three kinds of RTC interrupt: alarm interrupts, periodic interrupts, and carry interrupts.
An alarm interrupt request (ATI) is generated when the alarm flag (AF) in RCR1 is set to 1 while
the alarm interrupt enable bit (AIE) is also set to 1.
A periodic interrupt request (PRI) is generated when the periodic interrupt enable bits (PES2–
PES0) in RCR2 are set to a value other than 000 and the periodic interrupt flag (PEF) is set to 1.
A carry interrupt request (CUI) is generated when the carry flag (CF) in RCR1 is set to 1 while the
carry interrupt enable bit (CIE) is also set to 1.
11.5

Usage Notes

11.5.1

Register Initialization

After powering on and making the RCR1 register settings, reset the frequency divider (by setting
RCR2.RESET to 1) and make initial settings for all the other registers.
11.5.2

Carry Flag and Interrupt Flag in Standby Mode

When the carry flag or interrupt flag is set to 1 at the same time this LSI transits to normal mode
from standby mode by a reset or interrupt, the flag may not be set to 1. After exiting standby
mode, check the counters to judge the flag states if necessary.
11.5.3

Crystal Oscillator Circuit

Crystal oscillator circuit constants (recommended values) are shown in table 11.3, and the RTC
crystal oscillator circuit in figure 11.5.

Table 11.3 Crystal Oscillator Circuit Constants (Recommended Values)

f
osc
32.768 kHz
C
in
10–22 pF
C
out
10–22 pF
Rev. 3.0, 04/02, page 285 of 1064