CAT705, CAT706, CAT813

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9

APPLICATION NOTES

mP’s with Bidirectional Reset Pins

The RESET output can be pulled low by processors like

the 68HC11 allowing for a system reset issued by the

processor. The maximum pullup current that can be sourced

by the CAT705 & CAT706 1.5 mA (and by the CAT706

T/R/S is 800

mA) allowing the processor to pull the output

low even when the CAT70x is pulling it high.

Power Transients

Generally short duration negative−going transients of less

than 2

cause a reset condition. However the lower the voltage of the

transient the shorter the required time to cause a reset output.

These issues can usually be remedied by the proper location

of bypass capacitance on the circuit board.

Output Valid Conditions

The RESET output uses a push−pull output which can

current below 0.8 V a resistor can be connected from

RESET to Ground (see Figure 11.) This arrangement will

maintain a valid value on the RESET output during both

power up and down but will draw current when the RESET

output is in the high state. A resistor value of about 100 k

W

should be adequate in most situations to maintain a low

mC

WDI

GND

PFI

CAT705

CAT706

CAT813

100 kW

RESET/RESET

RESET/RESET

PFO

WDO

MR

mC

I/O LINE

INTERRUPT

NMI

VCC

Push Switch

5 V

WDI

GND

PFI

CAT705

CAT706

CAT813

UNREGULATED DC

Figure 12. Typical Operating Circuit

MR

PFO

WDO

RESET/RESET

RESET/RESET