MB89190/190A series
Chapter 3 CPU
3-39
3.7 Standby Mode (Low Power Consumption)
3.7.3 Stop Mode
The operation of the stop mode is explained.
T Operation of stop mode
Transition to stop mode
The stop mode stops the original oscillation.
Data in registers and RAM just before transition to the stop mode is held, and all functions except the
external interrupt are stopped. Consequently, data can be held at the minimum power consumption.
Control transits to the stop mode when 1 is written to the standby control register stop bit (STBC:
STP). At this point, when the pin state specification bit (STBC: SPL) is 0, the state of the external pin
is retained; when it is 1, the state of the external pin is set to high impedance (pin selecting pull-up
resistor ‘provided’ by option setting set to H level). When an interrupt request occurs at the instant 1 is
written to the STP bit, the write is ignored, control does not transit to the stop mode, and instruction
execution continues (control does not transit to stop mode even after interrupt processing). To transit
control to the stop mode, disable the time-base timer interrupt request output (TBTC: TBIE = 0) as
necessary.
Canceling stop mode
The stop mode is cancelled by a reset or an external interrupt.
For a product with the power-on reset ‘provided’, when a reset occurs in the stop mode, the reset
operation is performed after the elapse of the oscillation stabilization wait time. For a product with the
power-on reset ‘not provided’, the oscillation stabilization wait time is not used for a reset that occurs
at power-on or in the stop mode is enabled. The state of the pins is initialized by a reset. When an
interrupt request from an external interrupt circuit with a level higher than 11 occurs in the stop mode,
the stop mode is cancelled irrespective of the CPU interrupt enable flag (CCR: I) or interrupt level bits
(CCR: IL1, 0). In the stop mode, the resource(s) are stopped, so no interrupt requests other than
external interrupts occur. After the cancellation, the normal interrupt operation is performed after the
elapse of the oscillation stabilization wait time; when the interrupt is accepted, the interrupt processing
is performed, and when the interrupt is not accepted, the processing is executed starting with the
instruction immediately after the instruction executed just before transition to the stop mode. When
the stop mode is cancelled by an external interrupt, some of the resource(s) start operation, so the
interval timer function initial time interval, etc., becomes undefined.
Initialize each resource after
control returns from the stop mode.
Check: An interrupt to cancel the stop mode is only caused by interrupt requests from external interrupt
circuits.