UPSD3422 datasheet(83/293 Pages) STMICROELECTRONICS

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uPSD34xx

Supervisory functions

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Supervisory functions

Supervisory circuitry on the MCU Module will issue an internal reset signal to the MCU

Module and simultaneously to the PSD Module as a result of any of the following four

events:

●

The external RESET_IN pin is asserted

●

The Low Voltage Detect (LVD) circuitry has detected a voltage on VCC below a specific

threshold (power-on or voltage sags)

●

The JTAG Debug interface has issued a reset command

●

The Watch Dog Timer (WDT) has timed out

The resulting internal reset signal, MCU_RESET, will force the 8032 into a known reset state

while asserted, and then 8032 program execution will jump to the reset vector at program

address 0000h just after MCU_RESET is deasserted. The MCU Module will also assert an

active low internal reset signal, RESET, to the PSD Module. If needed, the signal RESET

can be driven out to external system components through any PLD output pin on the PSD

Module. When driving this “RESET_OUT” signal from a PLD output, the user can choose to

make it either active-high or active-low logic, depending on the PLD equation.

19.1

External reset input pin, RESET_IN

The RESET_IN pin can be connected directly to a mechanical reset switch or other device

which pulls the signal to ground to invoke a reset.

RESET_IN is pulled up internally and enters a Schmitt trigger input buffer with a voltage

hysteresis of VRST_HYS for immunity to the effects of slow signal rise and fall times, as

shown in Figure 23. RESET_IN is also filtered to reject a voltage spike less than a duration

of tRST_FIL. The RESET_IN signal must be maintained at a logic '0' for at least a duration of

tRST_LO_IN while the oscillator is running. The resulting MCU_RESET signal will last only as

long as the RESET_IN signal is active (it is not stretched). Refer to the Supervisor AC

specifications in Table 178 on page 279 at the end of this document for these parameter

values.

Figure 23.

Supervisor reset generation

MCU

Clock

Sync

Noise Filter

VCC

PULL-UP

DELAY,

tRST_ACTV

AI09603

RESET_IN

RESET

to PSD Module

MCU_RESET

to MCU and

Peripherals

LVD

JTAG Debug

WDT

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