NEC PD78214 - Manual (Page 406)

377
14
CHAPTER 14 STANDBY FUNCTION
14.1 FUNCTION OVERVIEW
The µPD78214 supports a standby function to reduce the system’s power consumption. With the standby function,
two modes are available:
• HALT mode: In this mode, only the CPU clock is stopped. Intermittent operation, when combined with normal
operating mode, can reduce overall system power consumption.
• STOP mode: In this mode, the oscillator is stopped to stop the entire system. Since only leakage currents are
allowed to flow in this mode, the system’s power consumption is minimized.
Each mode is specified by software. Fig. 14-1 is the transition diagram for the standby modes (STOP and HALT
modes).
Fig. 14-2 shows the functional block that implements the standby functions.
Fig. 14-1 Transition Diagram for the Standby Modes
Program
operation
Macro
service
HALT
(standby)
STOP
(standby)
Interrupt request
when interrupts
are disabled Vectored interrupt
request
Note 1
Set HALT
Input RESET Input NMI Vectored interrupt request
Note 2
Set STOP
Input RESET
Input NMI
Macro service
request
1-byte transfer
End of data transfer
Note 3
Macro service
request
1-byte transfer
End of data transfer
Note 4
Notes 1. When a vectored interrupt with a low priority is requested when it is disabled at the start of HALT mode
2. When a vectored interrupt with a high priority is requested, or when a vectored interrupt with a low priority is requested when it
is enabled at the start of HALT mode
3. When a macro service with a low priority is requested when low-priority interrupts are disabled at the start of HALT mode
4. When a macro service with a high priority is requested, or when a macro service with a low priority is requested while low-priority
interrupts are enabled at the start of HALT mode