HD404654 Datasheet, PDF (50/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404654 Series
Timer A
Timer A Functions: Timer A has the following functions.
• Free-running timer
The block diagram of timer A is shown in figure 33.
Timer A interrupt
request flag
(IFTA)
Selector
Clock
Timer
counter A
(TCA) ^Overflow
System
clock
ø _PER
Prescaler S (PSS)
3
Timer mode
register A
(TMA)
Figure 33 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: $001, bit 2). Timer A continues to be incremented after
reset to $00, and therefore it generates regular interrupts every 256 clocks.
Registers for Timer A Operation: Timer A operating modes are set by the following registers.
• Timer mode register A (TMA: $008): Four-bit write-only register that selects timer A’s operating mode
and input clock source as shown in figure 34.
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