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ML66525 Family User’s Manual
Chapter 3
CPU Control Functions
3 - 7
3.2.3 Examples of Standby Function Register Settings
HALT mode setting
(1)
Standby control register (SBYCON)
Setting bit 1 (HLT) to “1” changes the mode to the HALT mode.
STOP mode setting
(1)
Stop code acceptor (STPACP)
Write n5H, nAH (n = 0 to F) consecutively.
(2)
Standby control register (SBYCON)
If output ports are to be high impedance during the STOP mode, set bit 2 (FLT) to “1”.
If
oscillation of the main clock (OSCCLK) is not to be terminated during the STOP mode, reset
bit 3 (OSCS) to “0”.
To terminate oscillation of the main clock (OSCCLK), set bit 3 (OSCS)
to “1” and specify with bits 4 and 5 (OST0 and OST1) the oscillation stabilization time after
the main clock resumes.
Setting bit 0 (STP) to “1” changes the mode to the STOP mode.
3.2.4 Operation of Each Standby Mode
(1)
HALT mode
Setting bit 1 (HLT) of the standby control register (SBYCON) to “1” changes the mode to the
HALT mode.
In the HALT mode, the clock (CPUCLK) supply to the CPU is terminated, but the clock
(CPUCLK) is supplied to internal peripheral modules (TBC, WDT, general-purpose 8/16-bit
timers, serial ports, etc.) so their operation continues.
Because the CPU is halted, instructions
are not executed.
Instruction execution stops at the beginning of the next instruction
(following the instruction that set bit 1 (HLT) of SBYCON to “1”).
HALT mode is released when any of the following occurs: an interrupt request, reset by the
RESn pin input, or reset by overflow of the watchdog timer.
When HALT mode is released due to an interrupt request, if the interrupt is non-maskable, the
HALT mode is released unconditionally, and the CPU processes the non-maskable interrupt.
In the case of a maskable interrupt, the interrupt is released when both the interrupt request flag
(IRQ bit) and the interrupt enable flag (IE bit) have been set to “1”.
After the HALT mode is
released, if the master interrupt enable flag (MIE in PSW) has been set to “1”, processing of
the requested maskable interrupt is performed.
If the master interrupt enable flag (MIE in
PSW) has been reset to “0”, the next instruction (following the instruction that set the HALT
mode (that set bit 1 (HLT) of SBYCON to “1”)) is executed.
If the HALT mode is released by reset due to the RESn pin input or overflow of the watchdog
timer, the CPU will perform the reset processing.