HD404459 Datasheet, PDF (60/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
Timer A
Timer A Functions: Timer A (figure 41) has the following functions.
• Free-running timer
• Clock time-base
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
Prescaler S (PSS)
3
Timer mode
register A
(TMA)
Figure 41 Block Diagram of Timer A
Timer A Operations:
• Free-running timer operation: The input clock for timer A is selected by timer mode register A (TMA:
$008).
Timer A is reset to $00 by MCU reset and incremented at each input clock. If an input clock is applied
to timer A after it has reached $FF, an overflow is generated, and timer A is reset to $00. The overflow
sets the timer A interrupt request flag (IFTA: $002, bit 0). Timer A continues to be incremented after
reset to $00, and therefore it generates regular interrupts every 256 clocks.
• Clock time-base operation: Timer A is used as a clock time-base by setting bit 3 (TMA3) of timer mode
register A (TMA: $008) to 1. The prescaler W output is applied to timer A, and timer A generates
interrupts at the correct timing based on the 32.768-kHz crystal oscillation. In this case, prescaler W and
timer A can be reset to $00 by software.
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