Maxim Integrated Secure Microcontroller - Manual (Page 65)

Secure Microcontroller User’s Guide
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Figure 7-1. Secure Microcontroller Power Cycling Timing
7.5 Total Power Failure
If V
CC
voltage should fall below the V
CCMIN
threshold, processor operation halts. This is done by first
placing the CPU in a reset condition and then stopping the internal clock oscillator circuit, as illustrated in
Figure 7-1 . At this time the interface to the program/data RAM is disabled by pulling the CE line high.
This action guarantees an orderly shutdown for the lithium-backed RAM.
The microprocessor is automatically placed in the data retention state if V
CC
voltage drops below V
LI
; the
control circuitry accomplishes this by switching the internal power-supply line (V
CCI
) from pin to the
lithium power source. At this time, data is retained and no power is drawn from V
CC
.
When power is once again applied to the system, the V
CC
voltage eventually crosses the V
LI
threshold.
When this action is detected, the microprocessor automatically switches its internal supply line from the
lithium source back to the V
CC
pin. When V
CC
voltage eventually goes above the V
CCMIN
threshold, the