HD404449 Datasheet, PDF (32/123 Pages) Hitachi Semiconductor – HD404449 SERIES

HD404449 Series
Active mode
Watch mode
Oscillation
stabilization period
Active mode
Interrupt strobe
INT₀
Interrupt request
generation
(During the transition
from watch mode to
active mode only)
T
T
t _RC
Tx
T: Interrupt frame length
t_RC : Oscillation stabilization period
Figure 17 Interrupt Frame
Subactive Mode: The OSC₁ and OSC₂ oscillator stops and the MCU operates with a clock generated by
the X1 and X2 oscillator. In this mode, functions other than A/D conversion operate. However, because
the operating clock is slow, the power dissipation becomes low, next to watch mode.
The CPU instruction execution speed can be selected as 244 µs or 122 µs by setting bit 2 (SSR2) of the
system clock select register (SSR: $029). Note that the SSR2 value must be changed in active mode. If the
value is changed in subactive mode, the MCU may malfunction.
When the STOP or SBY instruction is executed in subactive mode, the MCU enters either watch or active
mode, depending on the statuses of the low speed on flag (LSON: $020, bit 0) and the direct transfer on
flag (DTON: $020, bit 3).
Subactive mode is an optional function that the user must specify on the function option list.
Interrupt Frame: In watch and subactive modes, ø_CLK is applied to timer A and the INT₀ circuit. Prescaler
W and timer A operate as the time-base and generate the timing clock for the interrupt frame. Three
interrupt frame lengths (T) can be selected by setting the miscellaneous register (MIS: $00C) (figure 18).
In watch and subactive modes, the timer-A/INT₀ interrupt is generated synchronously with the interrupt
frame. The interrupt request is generated synchronously with the interrupt strobe timing except during
transition to active mode. The falling edge of the INT₀ signal is input asynchronously with the interrupt
frame timing, but it is regarded as input synchronously with the second interrupt strobe clock after the
falling edge. An overflow and interrupt request in timer A is generated synchronously with the interrupt
strobe timing.
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