
S3C880A/F880A
RESET
RESET and POWER-DOWN
8-5
POWER-DOWN MODES
STOP MODE
Stop mode is invoked by the instruction Stop (opcode 7FH) however Stop available state must be set by value
"10100101b" in "STCON" register before Stop instruction is invoked. If Stop instruction (opcode 7FH) is executed
in Stop not available state (STCON = other value except "10100101b") CPU go to RESET address. After Stop
instruction is executed the state return to Stop not available state.
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 maximum 10 A. 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 signal or by an external interrupt.
Using
RESET
RESET to Release Stop Mode
Stop mode is released when the
RESET signal goes inactive (High level) from active (Low level) state.
All system and peripheral control registers are reset to their default 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 address stored in the ROM location 0100H.
Using an External Interrupt to Release Stop Mode
Two kinds of external interrupts with an RC-delay noise filter circuit can be used to release Stop mode. One
external interrupts in the S3C880A/F880A interrupt structure that meet this requirement are INT0–INT3 (P1.0–
P1.3) and the other one is V-sync input. Which interrupt you can use to release Stop mode in a given situation
depends on the microcontroller's current internal operating mode.
Note that when Stop mode is released by an external interrupt, the current values in system and peripheral
control registers are not changed. When you use an interrupt to release Stop mode, the CLKCON.3 and
CLKCON.4 register values remain unchanged, and the currently selected clock value is used. 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.
The external interrupt is serviced when a Stop mode release occurs. Following the IRET from the service routine,
the instruction immediately following the one that initiated Stop mode is executed.