HD404669 Datasheet, PDF (35/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit


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Stop Mode: In stop mode, all MCU operations stop and RAM data is retained. Therefore, the power
dissipation in this mode is the least of all modes. The OSC₁ and OSC₂ oscillator stops. For the X1 and X2
oscillator to operate or stop can be selected by setting bit 3 of the system clock select register 1 (SSR1:
$029; operating: SSR13 = 0, stop: SSR3 = 1) (figure 24). The MCU enters stop mode if the STOP
instruction is executed in active mode when bit 3 of timer mode register A (TMA: $008) is set to 0 (TMA3
= 0) (figure 40).
Stop mode is cleared by a RESET or STOPC* input. The RESET or STOPC input must be held for at least
the oscillation stabilization time (t _RC) as shown in figure 16. (refer to the "AC Characteristics" section.) In
either of these cases, the MCU will start program execution from the program start address (location 0).
However, the value of the RAM enable flag (RAME: $021,3) will be different in these cases. In particular,
RAME will be set to 0 for a RESET input and will be set to 1 for a STOPC input.
Also note that while a RESET input is effective in all MCU modes, STOPC is only effective in stop mode,
and is ignored in all other modes.
If a program needs to determine if stop mode was cleared by a STOPC input (for example, if the program
intends to use the contents of RAM that were stored before stop mode was entered after returning to active
mode) the program should test the RAM enable flag with a TEST instruction at the start of the program.
Note: * If stop mode is to be cleared by a STOPC input, applications should set bit 2 of port mode
register C (PMRC) to 1 (PMRC2 = 1) before switching to stop mode.
Oscillator
Internal
clock
Stop mode
RESET
STOPC
STOP instruction execution
t_res
(at least equal to oscillation stabilization time t_RC)
Figure 16 Timing of Stop Mode Cancellation
Watch Mode: In watch mode, the clock function (timer A) using the X1 and X2 oscillator, but other
function operations stop. Therefore, the power dissipation in this mode is the second least to stop mode,
and this mode is convenient when only clock display is used. In this mode, the OSC₁ and OSC₂ oscillator
stops, but the X1 and X2 oscillator operates. The MCU is switched to watch mode by executing a STOP
instruction while TMA3 = 1 in active mode, or by executing a STOP/SBY instruction while LSON is set to
1 or DTON is cleared to 0 in subactive mode.
Watch mode is terminated by a RESET input or a timer-A/INT₀ interrupt request. For details of RESET
input, refer to the Stop Mode section. When terminated by a timer-A/INT₀ interrupt request, the MCU
enters active mode if LSON = 0, or subactive mode if LSON = 1. After an interrupt request is generated,
the time required to enter active mode is t_RC for a timer A interrupt, and T_X (where T + t_RC < T_X < 2T +
t_RC) for an INT₀ interrupt, as shown in figures 17 and 18.
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