User`s manual

BL1600128 s Power Management
Figure H-2 shows the power-failure sequence.
Figure H-2. Power-Failure Sequence
Of course, if the DC input voltage continues to decrease, then the control-
ler will just power down. The routine calls hitwd to make sure that the
watchdog does not time out and thereby reset the processor. The controller
can continue to run, after a fashion, at low voltages, and might not be able
to detect the low-voltage condition because the Z180s /NMI input needs to
see a high-to-low transition edge.
A situation similar to a brownout will occur if the power supply is over-
loaded. In such a case, when a high-current load turns on, the raw voltage
supplied to the Z180 may dip below 7.9 V. In response, the interrupt
routine does a shutdown. This shutdown turns off the high-current load,
clearing the problem. However, if the cause of the overload persists, the
system will hunt, alternately experiencing an overload and then resetting.
To correct this situation, you must get a larger power supply.
1.0
2.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
I
Unregulated
DC
Regulated
+5 V
691
Asserts
PFO
691
Asserts
RESET
691
Ceases
Operation
t
H
Power
Fails
Time
C
Slope =
C/-I
Dropout
Voltage
Voltage (V)