NEC PD78P214 Manuale Utente

377

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.

Program
operation     

Macro 
service

HALT
(standby)

STOP  
(standby)

Interrupt request
when interrupts
are disabled

Vectored interrupt
request

Set HALT

Input RESET Input NMI 

Vectored interrupt request

 

Set STOP

Input RESET

Input NMI

Macro service 

request

1-byte transfer

End of data transfer

Macro service 

request

1-byte transfer

End of data transfer

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