USER'S GUIDE

The original contents of those Special Function regis- ters that are initialized by a reset are lost.

Voltage Monitoring Circuitry

The on±chip voltage monitoring circuitry automatically places the microprocessor in its Data Retention state in the absence of VCC. It insures that the proper internal control signals are generated and that power from the lithium cell is applied at the proper times so that the Pro- gram/Data RAM, data in the Scratchpad Registers and certain Special Function Registers remain unchanged when VCC is cycled on and off. In addition, an interrupt is available for signaling the processor of an impending

power fail condition so that the operational state of the processor can be saved just prior to entering the Data Retention.

The voltage monitoring circuitry recognizes three volt- age thresholds below nominal operating voltage. These thresholds are identified as VPFW (Power Fail Warning voltage), VCCmin (minimum operating voltage), and VLI (lithium supply) voltage. These thresholds are used to initiate required actions within the microprocessor dur- ing situations when VCC power is cycled on and off. The timing diagram shown in Figure 7±2 illustrates key inter- nal activities during power cycling.

SECURE MICROCONTROLLER POWER CYCLING TIMING Figure 7±2

VCC

VPFW

VCCMIN

VLI

tF

INTERRUPT

SERVICE

ROUTINE

tCSU

CLOCK

OSC.

tPOR

INTERNAL

RESET

LITHIUM

CURRENT

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Mitsubishi DS907x SIP, DS5000TK manual Voltage Monitoring Circuitry, Secure Microcontroller Power Cycling Timing ±2