Samsung S3C9228/P9228, 8-Bit CMOS Microcontroller user manual Using Reset to Release Stop Mode

RESET and POWER-DOWN S3C9228/P9228

POWER-DOWN MODES

STOP MODE

Stop mode is invoked by the instruction STOP. In Stop mode, the operation of the CPU and main oscillator is halted. All peripherals which the main oscillator is selected as a clock source stop also because main oscillator stops. But the watch timer and LCD controller will not halted in stop mode if the sub clock is selected as watch timer clock source. The data stored in the internal register file are retained in stop mode. Stop mode can be released in one of three ways: by a system reset, by an internal watch timer interrupt (when sub clock is selected as clock source of watch timer), or by an external interrupt.

Example:	LD	STOPCON,#10100101B
	STOP
	NOP
	NOP
	NOP
	LD	STOPCON,#00000000B

NOTES

1.Do not use stop mode if you are using an external clock source because XIN input must be restricted internally to VSS to reduce current leakage.

2.In application programs, a STOP instruction must be immediately followed by at least three NOP instructions. This ensures an adequate time interval for the clock to stabilize before the next instruction is executed. If three or more NOP instructions are not used after STOP instruction, leakage current could be flown because of the floating state in the internal bus.

3.To enable/disable STOP instruction, the STOPCON register should be written with 10100101B/other values before/after stop instruction.

Using RESET to Release Stop Mode

Stop mode is released when the RESET signal goes active (Low level): all system and peripheral control registers are reset to their default hardware values and the contents of all data registers are retained. When the programmed oscillation stabilization interval has elapsed, the CPU starts the system initialization routine by fetching the program instruction stored in ROM location 0100H.

Using an External Interrupt to Release Stop Mode

External interrupts can be used to release stop mode. For the S3C9228 microcontroller, we recommend using the INT interrupt, P0, P1, and P3.

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