Maxim Integrated Secure Microcontroller - Manual (Page 180)

Secure Microcontroller User’s Guide
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battery-backed.
PE3 and PE4 are not backed, and can be connected to normal circuits. On the DS5000FP,
CE1, CE2, and BA14 are battery-backed.
Negative Voltage Spikes. Do not allow negative voltage to contact the device. This includes under
shoots on power or ports, static, plugging in backwards, or applying a signal without a common ground
reference. Electrostatic discharge can also produce momentary negative voltages.
Do’s
Use Static Protection. Do use Schottky diodes and resistors on port pins that are available at the
outside world. Static can represent a negative voltage that temporarily collapses the battery voltage. This
is discussed in Application Note 93: Design Guidelines for Microcontrollers Incorporating NV RAM.
Design In-System Programmability Into the Design. Do provide a method of in-system loading,
such as an RS-232 transceiver, a connector, and a way to invoke the loader. This is especially important
to applications that employ physical security, such as those encased in epoxy or tripwires.
Use the Watchdog Timer. Even the best-designed microprocessor system occasionally encounters
situations that may corrupt processor operation. The watchdog is the first line of defense. If software runs
out of control, it can only do so for the duration of one watchdog timeout before the device resets.
Control the Power Supply. The best of all scenarios is when a power-down occurs under control of
the microprocessor software. If the power switch actually asks software to turn the power off, then
software is never taken by surprise. Also, ensure the power-supply slew rate meets the value specified in
the part’s corresponding data sheet.