Hardware manual

Rev. 3.0, 09/98, page 270 of 361
15.4.3 Sample Application of Software Standby Mode
In this example the chip enters the software standby mode when NMI goes Low and exits when
NMI goes High, as shown in figure 15.1.
The NMI edge bit (NMIEG) in the system control register is originally cleared to “0,” selecting
the falling edge. When NMI goes Low, the NMI interrupt handling routine sets NMIEG to “1,”
sets SSBY to “1” (selecting the rising edge), then executes the SLEEP instruction. The chip enters
the software standby mode. It recovers from the software standby mode on the next rising edge of
NMI.
Clock
generator
Ø
NMI
NMIEG
SSBY
NMI interrupt handler
NMIEG = "1"
SSBY = "1"
Software standby mode
(power-down state)
SLEEP
NMI interrupt
handler
Settling time
Figure 15.1 NMI Timing in Software Standby Mode