h8s-2169 Renesas Electronics Corporation., h8s-2169 Datasheet - Page 452

• Manufacturer Part Number: h8s-2169
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2100 Series
• Manufacturer: Renesas Electronics Corporation.

Section 14 Watchdog Timer (WDT)
14.5.5
If the mode is switched between high-speed mode and subactive mode or between high-speed
mode and watch mode when WDT1 is used as a realtime clock counter, an error will occur in the
counter value when the internal clock is switched.
When the mode is switched from high-speed mode to subactive mode or watch mode, the
increment timing is delayed by approximately 2 or 3 clock cycles when the WDT1 control clock is
switched from the main clock to the subclock.
Also, since the main clock oscillator is halted during subclock operation, when the mode is
switched from watch mode or subactive mode to high-speed mode, the clock is not supplied until
internal oscillation stabilizes. As a result, after oscillation is started, counter incrementing is halted
during the oscillation stabilization time set by bits STS2 to STS0 in SBYCR, and there is a
corresponding discrepancy in the counter value.
Caution is therefore required when using WDT1 as the realtime clock counter.
No error occurs in the counter value while WDT1 is operating in the same mode.
14.5.6
To clear OVF flag in WOVI handling routine, read TCSR when OVF=1, then write with 0 to
OVF, as stated above.
When WOVI is masked and OVF flag is poling, if contention between OVF flag set and TCSR
read is occurred, OVF=1 is read but OVF can not be cleared by writing with 0 to OVF.
In this case, reading TCSR when OVF=1 two times meet the requirements of OVF clear condition.
Please read TCSR when OVF=1 two times before writing with 0 to OVF.
Rev. 3.00 Jan 18, 2006 page 424 of 1044
REJ09B0280-0300
Counter Value in Transitions between High-Speed Mode, Subactive Mode, and
Watch Mode
OVF Flag Clear Condition
LOOP
BTST.B
BEQ
MOV.B
MOV.W
MOV.W
#7,@TCSR
LOOP
@TCSR,R0L ; OVF=1 read again
#H'A521,R0
R0,@TCSR
; OVF flag read
; if OVF=1, exit from loop
; OVF flag clear
;
: