MC68HC705K1 Datasheet, PDF (23/140 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
General Description
Pin Assignments
disconnects the internal startup resistor. The PIN3 bit in the mask option
register must remain erased (logic 0). The PIN3 bit selects the 3-pin RC
oscillator configuration. See 9.6 Mask Option Register.
1.6.2.4 3-Pin RC Oscillator
Another low-cost option is the 3-pin RC oscillator configuration shown in
Figure 1-8. The 3-pin oscillator is more stable than the 2-pin oscillator.
The OSC2 and PB1/OSC3 signals are square waves, and the signal on
OSC1 is a triangular wave. The 3-pin RC oscillator configuration is
recommended for frequencies of 1 MHz and less.
MCU
PB1/OSC3
C3
V_SS
OSC1
R
OSC2
+
R
C3
V_SS
C1 C2
V_DD
Figure 1-8. 3-Pin RC Oscillator Connections
To use the 3-pin RC oscillator configuration, both the RC and PIN3 bits
in the mask option register must be programmed to logic 1s. See
9.6 Mask Option Register.
NOTE:
In 3-pin RC oscillator configurations, the personality EPROM
(PEPROM) cannot be programmed by user software. If the voltage on
IRQ/V_PP is raised above V_DD, the oscillator will revert to a 2-pin oscillator
configuration and device operation will be disrupted.
1.6.2.5 External Clock
An external clock from another CMOS-compatible device can drive the
OSC1 input, with the OSC2 pin unconnected, as Figure 1-9 shows.
MC68HC705K1 — Rev. 2.0
General Description
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Technical Data