E202075_HD404889 Datasheet, PDF (84/202 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip LCD Circuit

HD404889/HD404899/HD404878/HD404868 Series
32.768-kHz
oscillator
1/4
1/2
f _{W Prescaler W}
t _Wcyc
(PSW)
2 f_W
1/2 t _Wcyc
Selector
Timer A interrupt
request flag
(IFTA)
Clock Timer
counter A
(TCA) ^Overflow
Selector
System
clock
ø _PER
Data bus
Clock line
Signal line
Prescaler S (PSS)
3
Timer mode
register A
(TMA)
Figure 35 Timer A Block Diagram
Timer A Operation
Free-running timer operation:
The timer A input clock is selected by timer mode register A (TMA: $00F).
Timer A is reset to $00 by an MCU reset, and counts up each time the input clock is input. When the input
clock is input after the timer A value reaches $FF, overflow output is generated, and the timer A value
becomes $00. The generated overflow output sets the timer A interrupt request flag (IFTA: $002,0). Timer
A continues counting up after the count value returns to $00, so that an interrupt is generated regularly
every 256 input clock cycles.
Realtime clock time base operation:
Timer A can be used as the realtime clock time base by setting bit 3 (TMA3) of timer mode register A to 1.
As the prescaler W output is input to timer/counter A, interrupts are generated with accurate timing using
the 32.768 kHz crystal oscillator as the basic clock.
When timer A is used as the realtime clock time base, prescaler W and timer/counter A can be reset to $00
by the program.
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