HD404449 Datasheet, PDF (57/123 Pages) Hitachi Semiconductor – HD404449 SERIES

Timer A
Timer A Functions: Timer A has the following functions.
• Free-running timer
• Clock time-base
The block diagram of timer A is shown in figure 40.
32.768-kHz
oscillator
1/4
1/2
f _{W Prescaler W}
tw_cyc
(PSW)
2 f_W
1/2 tw_cyc
Selector
System
clock
ø _PER
Selector
Prescaler S (PSS)
HD404449 Series
Timer A interrupt
request flag
(IFTA)
Clock Timer
counter A
(TCA) ^Overflow
3
Timer mode
register A
(TMA)
Figure 40 Timer A Block Diagram
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: $001, bit 2). 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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