NEC switch - Manual (Page 178)

User’s Manual U12978EJ3V0UD
178
CHAPTER 12 STANDBY FUNCTION
12.1 Standby Function and Configuration
12.1.1 Standby function
The standby function is used to reduce the power consumption of the system and can be effected in the following
two modes.
(1) HALT mode
This mode is set when the HALT instruction is executed. The HALT mode stops the operation clock of the CPU.
The system clock oscillator continues oscillating. This mode does not reduce the power consumption as much
as the STOP mode, but is useful for resuming processing immediately when an interrupt request is generated,
or for intermittent operations.
(2) STOP mode
This mode is set when the STOP instruction is executed. The STOP mode stops the system clock oscillator
and stops the entire system. The power consumption of the CPU can be substantially reduced in this mode.
The STOP mode can be released by an interrupt request, so that this mode can be used for intermittent
operations. However, some time is required until the system clock oscillator stabilizes after the STOP mode has
been released. If processing must be resumed immediately by using an interrupt request, therefore, use the
HALT mode.
In both modes, the previous contents of the registers, flags, and data memory before setting the standby mode
are all retained. In addition, the statuses of the output latches of the I/O ports and output buffers are also retained.
Caution To set the STOP mode, be sure to stop the operations of the peripheral hardware, and then
execute the STOP instruction.