MC68HC05T16
MOTOROLA
4-1
RESETS AND INTERRUPTS
4
4
RESETS AND INTERRUPTS
4.1
RESETS
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
Power-On Reset (POR)
The power-on reset occurs when a positive transition is detected on the supply voltage, V
DD
. The
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
DD
has risen to a point where the MCU can
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
DD
has risen to the minimum operating voltage
specified.
4.1.2
RESET Pin
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.
TPG
29
Summary of Contents for MC68HC05T16
Page 2: ......
Page 14: ...MOTOROLA vi MC68HC05T16 THIS PAGE LEFT BLANK INTENTIONALLY TPG 12 ...
Page 16: ...MOTOROLA viii MC68HC05T16 THIS PAGE LEFT BLANK INTENTIONALLY TPG 14 ...
Page 18: ...MOTOROLA x MC68HC05T16 THIS PAGE LEFT BLANK INTENTIONALLY TPG 16 ...
Page 54: ...MOTOROLA 5 12 MC68HC05T16 TIMERS 5 THIS PAGE LEFT BLANK INTENTIONALLY TPG 52 ...
Page 64: ...MOTOROLA 6 10 MC68HC05T16 M BUS SERIAL INTERFACE 6 THIS PAGE LEFT BLANK INTENTIONALLY TPG 62 ...
Page 110: ...MOTOROLA 12 4 MC68HC05T16 LOW POWER MODES 12 THIS PAGE LEFT BLANK INTENTIONALLY TPG 108 ...
Page 116: ...MOTOROLA 13 6 MC68HC05T16 OPERATING MODES 13 THIS PAGE LEFT BLANK INTENTIONALLY TPG 114 ...