The 80C320 provides two new
features to handle power failure conditions. The first feature
is an automatic power failure reset and the other is a power
Power Failure Reset
The 80C320 is equipped with an automatic power
failure reset. This means that if the operating voltage drops
below Vrst (see
spec sheet.) , the microcontoller will automatically enter a
reset mode. The chip will remain in reset mode until normal
operating voltage is restored. This reset is performed
automatically requiring no special action on the part of the
software or of the user.
This feature is important. A normal 8051, without such a
feature, continues to run "normally" as power dips below the
minimum. However, the 8051 may begin to execute bogus
instructions and/or starts writing/reading incorrect values to
and from memory locations. The power failure reset feature on
the 80320 prevents a low power condition from causing strange
and unexpected program behavior.
A new interrupt can be enabled which is
triggered when the operating voltage drops below Vpfi
chip spec sheet.) This can be useful to make preparations
for a power failure.
WDCON.5 (EPFI) is the enable for
the Power Failure Interrupt. When this bit is set, a low
operating voltage will trigger the interrupt. When the bit is
clear, the interrupt will not be triggered.
WDCON.4 (PFI) is the flag that is
set when the power falls below Vpfi. If the
interrupt is enabled (via bit EPFI), an interrupt will be
triggered when this bit is set. Even if the power failure
interrupt is not set, this bit will be set to reflect a
Once PFI is set by the hardware, software
must clear it manually. The bit will not be cleared
The interrupt vector for the power failure
interrupt is 0033h.