Samsung S3C84E5 user manual POWER-DOWN Modes, Using Reset to Release Stop Mode

S3C84E5/C84E9/P84E9 RESET and POWER-DOWN

POWER-DOWN MODES

STOP MODE

Stop mode is invoked by the instruction STOP (opcode 7FH). In Stop mode, the operation of the CPU and all peripherals is halted. That is, the on-chip main oscillator stops and the supply current is reduced to less than 3 µA except for the current consumption of LVR (Low voltage Reset) circuit. All system functions stop when the clock "freezes," but data stored in the internal register file is retained. Stop mode can be released in one of two ways: by a reset or by interrupts.

NOTE

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.

Using RESET to Release Stop Mode

Stop mode is released when the nRESET signal is released and returns to high level: all system and peripheral control registers are reset to their default hardware values and the contents of all data registers are retained. A reset operation automatically selects a slow clock (1/16) because CLKCON.3 and CLKCON.4 are cleared to '00B'. After the programmed oscillation stabilization interval has elapsed, the CPU starts the system initialization routine by fetching the program instruction stored in ROM location 0100H (and 0101H).

Using an External Interrupt to Release Stop Mode

External interrupts with an RC-delay noise filter circuit can be used to release Stop mode. Which interrupt you can use to release Stop mode in a given situation depends on the microcontroller's current internal operating mode. The external interrupts in the S3C84E5/C84E9/P84E9 interrupt structure that can be used to release Stop mode are:

— External interrupts P2.0–P2.7 (INT0–INT7) and P4.0–P4.2 (INT8–INT10)

Please note the following conditions for Stop mode release:

—If you release Stop mode using an external interrupt, the current values in system and peripheral control registers are unchanged.

—If you use an 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.

—When the Stop mode is released by external interrupt, the CLKCON.4 and CLKCON.3 bit-pair setting remains unchanged and the currently selected clock value is used.

—The 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.

Using an internal Interrupt to Release Stop Mode

Activate any enabled interrupt, causing stop mode to be released. Other things are same as using external interrupt.

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