H8SXSLASH1663M datasheet(886/1504 Pages) RENESAS

886 / 1504 page

Section 17 32K Timer (TM32K)

Rev. 2.00 Sep. 24, 2008 Page 854 of 1468

REJ09B0412-0200

17.5

Usage Notes

17.5.1

Changing Values of Bits EXCKSN, CKS1, and CKS0

If bits EXCKSN, CKS1, and CKS0 in TCR32K are written to while the TM32K is operating,

errors could occur in the incrementation. The TM32K must be stopped (the TME bit is set to 0)

before the values of bits EXCKSN, CKS1, and CKS0 are changed.

Note that when the EXCKSN bit is 0, the CKS1 bit can be changed even though the TME bit is 1

(see section 17.3.3, EXCKSN=0 Operation).

17.5.2

Note on Register Initialization

TCR32K, TCNT32K1, TCNT32K2, and TCNT32K3 of the 32K timer are initialized in hardware

standby mode or in the pin reset state. A reset from the watchdog timer or deep-software-standby

reset does not initialize these registers.

17.5.3

Usage Notes on 32K Timer

• The 32K timer does not operate when the OSC32STP bit is set to 1. Always set the

OSC32STP bit to 0 when starting the 32K timer.

• When the OSC32STP bit has been changed from 1 to 0, allow enough time to ensure settling

of the oscillation by the subclock oscillator.

• Before stopping the TM32K, clear the TME bit to 0 for one clock (30 µs) or longer by the 32

subclock.

• When switching between subclock and main clock operation, wait for 500 µs or more (until

the timer counter is updated next time) before reading the timer counter.

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