Resets And Interrupts; Resets; Power-On Reset (Por); Reset Pin - Motorola MC68HC05T16 Technical Data Manual

Table of Contents

RESETS AND INTERRUPTS

4.1

The MC68HC05T16 can be reset in three ways: by the initial power-on reset function, by an active

low input to the RESET pin, and by a COP watchdog timer reset (if enabled). Any of these resets

will cause the program to go to its starting address, speciﬁed by the contents of memory locations

$FFFE and $FFFF, and cause the interrupt mask of the Condition Code register to be set.

4.1.1

The power-on reset occurs when a positive transition is detected on the supply voltage, V

power-on reset is used strictly for power-up conditions, and should not be used to detect any drops

in the power supply voltage. There is no provision for a power-down reset. The power-on circuitry

provides for a 4064 tcyc delay from the time that the oscillator becomes active. If the external

RESET pin is low at the end of the 4064 tcyc time out, the processor remains in the reset condition

until RESET goes high. The user must ensure that V

operate properly prior to the time the 4064 POR cycles have elapsed. If there is doubt, the external

RESET pin should remain low until such time that V

speciﬁed.

4.1.2

The RESET input pin is used to reset the MCU to provide an orderly software start-up procedure.

When using the external reset, the RESET pin must stay low for a minimum of 1.5tcyc. The

RESET pin contains an internal Schmitt Trigger as part of its input to improve noise immunity.

MC68HC05T16

has risen to a point where the MCU can

has risen to the minimum operating voltage

RESETS AND INTERRUPTS

. The

TPG

MOTOROLA

4-1

Table of Contents

Table of Contents

Mc68hc705t16