HD404369 Datasheet, PDF (56/117 Pages) Hitachi Semiconductor – 4-bit HMCS400-Series microcomputer

HD404369 Series
Timers
The MCU has four timer/counters (A to C).
• Timer A: Free-running timer
• Timer B: Multifunction timer
• Timer C: Multifunction timer
Timer A is an 8-bit free-running timer. Timers B and C are 8-bit multifunction timers, whose functions are
listed in table 25. The operating modes are selected by software.
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 36.
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.
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 37.
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