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S3C9228/P9228 RESETRESET and POWER-DOWN
8-3
Using an Internal Interrupt to Release Stop Mode
An internal interrupt, watch timer, can be used to release stop mode because the watch timer operates in stop
mode if the clock source of watch timer is sub clock. If system clock is sub clock, you can't use any interrupts to
release stop mode. That is, you had better use the idle instruction instead of stop one when sub clock is selected
as the system clock.
Please note the following conditions for Stop mode release:
— If you release stop mode using an internal or external interrupt, the current values in system and peripheral
control registers are unchanged.
— If you use an internal or external interrupt for stop mode release, you can also program the duration of the
oscillation stabilization interval. To do this, you must make the appropriate control and clock settings before
entering stop mode.
— If you use an interrupt to release stop mode, the bit-pair setting for CLKCON.4/CLKCON.3 remains
unchanged and the currently selected clock value is used.
— The internal or external interrupt is serviced when the stop mode release occurs. Following the IRET from
the service routine, the instruction immediately following the one that initiated stop mode is executed.
IDLE MODE
Idle mode is invoked by the instruction IDLE (opcode 6FH). In Idle mode, CPU operations are halted while some
peripherals remain active. During Idle mode, the internal clock signal is gated away from the CPU and from all
but the following peripherals, which remain active:
— Interrupt logic
— Basic timer
— Timer 1 (Timer A and B)
— Watch timer
— LCD controller
I/O port pins retain the mode (input or output) they had at the time Idle mode was entered.
Idle Mode Release
You can release Idle mode in one of two ways:
1. Execute a reset. All system and peripheral control registers are reset to their default values and the contents
of all data registers are retained. The reset automatically selects the slowest clock (1/16) because of the
hardware reset value for the CLKCON register. If all external interrupts are masked in the IMR register, a
reset is the only way you can release Idle mode.
2. Activate any enabled interrupt — internal or external. When you use an interrupt to release Idle mode,
the 2-bit CLKCON.4/CLKCON.3 value remains unchanged, and the currently selected clock value is
used. The interrupt is then serviced. When the return-from-interrupt condition (IRET) occurs, the
instruction immediately following the one which initiated Idle mode is executed.