SECTION 1: GENERAL DESCRIPTION
MOTOROLA
Page 11
MC68HC05V7 Specification Rev. 1.0
1.5.7.3
External Clock
An external clock from another CMOS-compatible device can be connected to the OSC1
input. The OSC2 pin should be left unconnected, as shown in
Figure 1-7(b).1.5.8
RESET
This pin can be used as an input to reset the MCU to a known start-up state by pulling it to
the low state. The RESET pin contains an internal Schmitt trigger to improve its noise
immunity as an input. The RESET pin has an internal pulldown device that pulls the RESET
pin low when there is an internal COP Watchdog reset, POR, illegal address reset, a
disabled STOP instruction reset, or an internal low voltage reset. Refer to
SECTION 61.5.9
IRQ (MASKABLE INTERRUPT REQUEST)
This input pin drives the asynchronous IRQ interrupt function of the CPU. The IRQ interrupt
function has a mask option to select either negative edge-sensitive triggering or both
negative edge-sensitive and low level-sensitive triggering. The IRQ input requires an
external resistor to V
DD for “wire-OR” operation, if desired. If the IRQ pin is not used, it must
be tied to the VDD supply. The IRQ pin contains an internal Schmitt trigger as part of its input
to improve noise immunity. Each of the PA0 thru PA7 and PC0 thru PC7 I/O pins may be
connected as an OR function with the IRQ interrupt function. This capability allows
keyboard scan applications where the transitions on the I/O pins will behave the same as
the IRQ pin. The edge or level sensitivity selected by a mask option for the IRQ pin does
not apply to the I/O pin interrupt. The I/O pin interrupt is always negative edge sensitive.
1.5.10
PA0-PA7
These eight I/O lines comprise Port A. The state of any pin is software programmable and
all Port A lines are configured as inputs during power-on or reset. All eight pins are
connected via an internal gate to the IRQ interrupt function. When the IRQ interrupt function
is enabled, all the Port A pins will act as negative edge sensitive IRQ sources. See
1.5.11
PB0-PB5, PB6/TCMP, PB7/TCAP
These eight I/O lines comprise Port B. The state of any pin is software programmable and
all Port B lines are configured as inputs during power-on or reset. See
SECTION 9PARALLEL I/O for more details on the I/O ports. PB6 and PB7 are also shared with timer
functions. The TCAP pin controls the input capture feature for the on-chip 16-bit timer. The
TCMP pin provides an output for the output compare feature of the on-chip 16-bit timer. See
1.5.12
PC0-PC7
These eight I/O lines comprise Port C. The state of any pin is software programmable and
all Port C lines are configured as inputs during power-on or reset. All eight pins are
connected via an internal gate to the IRQ interrupt function. When the IRQ interrupt function