NEC 78K0 User Manual page 449

(2) STOP mode
STOP instruction execution sets the STOP mode. In the STOP mode, the X1 oscillator stops, stopping the whole
system, thereby considerably reducing the CPU operating current.
Because this mode can be cleared by an interrupt request, it enables intermittent operations to be carried out.
However, because a wait time is required to secure the oscillation stabilization time after the STOP mode is
released, select the HALT mode if it is necessary to start processing immediately upon interrupt request
generation.
In either of these two modes, all the contents of registers, flags and data memory just before the standby mode is
set are held. The I/O port output latches and output buffer statuses are also held.
Cautions 1. STOP mode can be used only when CPU is operating on the X1 input clock or Ring-OSC
clock. HALT mode can be used when CPU is operating on the X1 input clock, Ring-OSC
clock, or subsystem clock. However, when the STOP instruction is executed during Ring-
OSC clock operation, the X1 oscillator stops, but Ring-OSC oscillator does not stop.
2. When shifting to the STOP mode, be sure to stop the peripheral hardware operation before
executing STOP instruction.
3. The following sequence is recommended for operating current reduction of the A/D converter
when the standby function is used: First clear bit 7 (ADCS) of the A/D converter mode
register (ADM) to 0 to stop the A/D conversion operation, and then execute the HALT or STOP
instruction.
4. If the Ring-OSC oscillator is operating before the STOP mode is set, oscillation of the Ring-
OSC clock cannot be stopped in the STOP mode. However, when the Ring-OSC clock is used
as the CPU clock, the CPU operation is stopped for 17/f
CHAPTER 21 STANDBY FUNCTION
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User's Manual U15947EJ2V0UD
(s) after STOP mode is released.
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