
RESET
RESET and POWER-DOWN
S3C8639/C863A/P863A/C8647/F8647
8-6
POWER-DOWN MODES
STOP MODE
Stop mode is invoked by the instruction STOP (opcode 7FH) and the stop control register (STOPCON). 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 5
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 or by an external
interrupt (with RC delay).
NOTE
Do not use stop mode if you are using an external clock source as X
IN input must be restricted internally
to V
SS to reduce current leakage.
Using
RESET
RESET to Release Stop Mode
Stop mode is released when the
RESET signal goes active (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 the ROM location 0100H (and 0101H).
Using an External Interrupt to Release Stop Mode
Only 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 S3C8639/C863A/C8647 interrupt structure that can be used to release Stop
mode are:
— External interrupts P0.0 (INT0), P0.1 (INT1), and P0.2 (INT2)
— Timer M0 capture interrupt in capture mode (with rising or falling edge trigger at the TM0CAP pin and
Vsync-O from sync-processor.)
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 control and clock settings appropriate before entering
Stop mode.
— If you use an interrupt to release Stop mode, 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 right next to the one that initiated Stop mode is executed.