HD404849 Datasheet, PDF (35/125 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404849 Series
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).
Interrupt Frame: In watch and subactive modes, φ_CLK is applied to timer A and theINT₀ 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, a timer-A/INT₀ interrupt is generated synchronously with the interrupt
frame. An interrupt request is generated synchronously with an interrupt strobe 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.
Direct Transition from Subactive Mode to Active Mode: Available by controlling the direct transfer on
flag (DTON: $020, bit 3) and the low speed on flag (LSON: $020, bit 0). The procedures are described
below:
• Set LSON to 0 and DTON to 1 in subactive mode.
• Execute the STOP or SBY instruction.
• The MCU automatically enters active mode from subactive mode after waiting for the MCU internal
processing time and oscillation stabilization time (figure 19).
Notes: 1. The DTON flag ($020, bit 3) can be set only in subactive mode. It is always reset in active
mode.
2. The transition time (T_D) from subactive mode to active mode:
t_RC < T_D < T + t_RC
STOP/SBY instruction execution
Subactive mode
MCU internal
processing period
(Set LSON = 0, DTON = 1)
Oscillation
stabilization
time
Active mode
Interrupt strobe
Direct transfer
completion timing
T
t _RC
T: Interrupt frame length
t _RC : Oscillation stabilization period
Figure 19 Direct Transition Timing
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