SH7721 datasheet(645/1524 Pages) RENESAS

645 / 1524 page

Section 17 Realtime Clock (RTC)

Rev. 3.00 Jan. 18, 2008 Page 583 of 1458

REJ09B0033-0300

17.5

Usage Notes

17.5.1

The following RTC registers cannot be written to during an RTC count (while bit 0 = 1 in RCR2).

RSECCNT, RMINCNT, RHRCNT, RDAYCNT, RWKCNT, RMONCNT, RYRCNT

The RTC count must be stopped before writing to any of the above registers.

17.5.2

Use of Realtime Clock (RTC) Periodic Interrupts

The method of using the periodic interrupt function is shown in figure 17.5.

A periodic interrupt can be generated periodically at the interval set by the flags PES0 to PES2 in

RCR2. When the time set by the PES0 to PES2 has elapsed, the PEF is set to 1.

The PEF is cleared to 0 upon periodic interrupt generation or when the flags PES0 to PES2 are set.

Periodic interrupt generation can be confirmed by reading this bit, but normally the interrupt

function is used.

Set PES0 to PES2,

and clear PEF to 0,

in RCR2

Clear PEF to 0

Set PES, clear PEF

Elapse of time set by PES

Clear PEF

Figure 17.5 Using Periodic Interrupt Function

17.5.3

Transition to Standby Mode after Setting Register

When a transition to standby mode is made after registers in the RTC are set, sometimes counting

is not performed correctly. In case the registers are set, be sure to make a transition to standby

mode after waiting for two RTC clocks or more.

SH7721 Datasheet(PDF) 645 Page - Renesas Technology Corp