Freescale Semiconductor, Inc.
Ge ne ra l De sc rip tion
1.6.5.3 Exte rna l Clo c k
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 1-3(b).
MCU
MCU
OSC1
OSC2
OSC1
OSC2
10 MΩ*
UNCONNECTED
20 pF *
20 pF *
4 MHz*
EXTERNAL CLOCK
(a) Crystal or Ceramic
Resonator Connections
(b)External Clock
Source Connection
*Values shown are typical. For further information, consult the crystal oscillator vendor.
Figure 1-3. Oscillator Connections
1.6.6 RESET
This pin can be used as an input to reset the MCU to a known startup
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 computer operating properly (COP) watchdog reset,
power-on reset (POR), illegal address reset, a disabled STOP
instruction reset or an internal low-voltage reset. Refer to
Section 5. Resets.
1.6.7 IRQ (Ma ska b le Inte rrup t Re q ue st)
This input pin drives the asynchronous IRQ interrupt function of the
CPU. The IRQ interrupt function has a programmable 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 for wire-OR operation, if desired. If the IRQ pin
DD
is not used, it must be tied to the V supply. The IRQ pin contains an
DD
General Release Specification
MC68HC05V12 — Rev. 1.0
General Description
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