NEC PD78F9488 - Manual (Page 307)

User’s Manual U15331EJ4V1UD
307
CHAPTER 17 STANDBY FUNCTION
17.1 Standby Function and Configuration
17.1.1 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 main system clock
oscillator and stops the entire system. The power consumption of the CPU can be substantially reduced in
this mode.
The data memory can be retained at a low voltage (V
DD
= 1.8 V). Therefore, this mode is useful for retaining
the contents of the data memory at an extremely low current.
The STOP mode can be released by an interrupt request, so that this mode can be used for intermittent
operation. 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.