
29
μ
PD78044H, 78045H, 78046H
7. STANDBY FUNCTION
The standby function is to reduce the current dissipation of the system and can be effected in the following two
modes:
HALT mode : In this mode, the operating clock of the CPU is stopped. By using this mode in combination with
the normal operation mode, the system can be operated intermittently, so that the average current
dissipation can be reduced.
STOP mode : Oscillation of the main system clock is stopped. All the operations on the main system clock are
stopped, and therefore, the current dissipation of the system can be minimized with only the
subsystem clock oscillating.
Fig. 7-1 Standby Function
Note
By stopping the main system clock, the current dissipation can be reduced. When the CPU operates on
the subsystem clock, stop the main system clock by setting bit 7 (MCC) of the processor clock control register
(PCC). The STOP instruction cannot be used.
Caution When the main system clock is stopped and the subsystem clock is operating, to switch again
from the subsystem clock to the main system clock, allow sufficient time for the oscillation to
settle before switching, by coding the program accordingly.
8. RESET FUNCTION
The system can be reset in the following two modes:
External reset by RESET pin
Internal reset by watchdog timer that detects hang up
STOP mode
(Oscillation of main system
clock stopped)
Main system
clock operation
Subsystem
clock operation
Note
HALT mode
(Clock supply to CPU stopped.
Oscillation continues)
HALT mode
Note
(Clock supply to CPU stopped.
Oscillation continues)
STOP
instruction
Interrupt
request
Interrupt
request
Interrupt
request
CSS=0
CSS=1
HALT instruction
HALT instruction