MC68HC05E0 Datasheet, PDF (18/96 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

recommended capacitance and feedback resistance values. The manufacturer of the particular
2
ceramic resonator being considered should be consulted for specific information.
2.2.3 External Clock
An external clock should be applied to the OSC1 input with the OSC2 pin not connected, as shown
in Figure 2-1(d). The tOXOV or tILCH specifications do not apply when using an external clock
input. The equivalent specification of the external clock source should be used in lieu of tOXOV or
tILCH.
2.3
RESET
This active low input-only pin is used to reset the MCU. Applying a logic zero to this pin forces the
device to a known start-up state. An external RC-circuit can be connected to this pin to generate
a power-on reset (POR). In this case, the time constant must be chosen high enough (minimum
100 ms) to allow the oscillator circuit to stabilise. This input has an internal pull-up resistor and an
internal Schmitt trigger to improve noise immunity.
2.4
Port A (PA0 - PA7)
Port A is comprised of eight bidirectional pins (PA0 to PA7). The direction and state of each pin is
software programmable, and each pin can drive one LED load. All pins are configured as inputs
during power-on or reset.
2.5
Port B (PB0 - PB7)
Port B is comprised of eight bidirectional pins (PB0 to PB7). The direction and state of each pin is
software programmable. All pins are configured as inputs during power-on or reset.
2.6
Port C (PC0 - PC7)
Port C is comprised of eight bidirectional pins (PC0 to PC7). The direction and state of each pin
is software programmable. In addition, each input can be configured to support a wake-up function
and trigger a processor interrupt. All pins are configured as inputs during power-on or reset.
MOTOROLA
2-2
FUNCTIONAL PIN DESCRIPTION
MC68HC05E0