Datasheet

MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
106 Oscillator Module (OSC) MOTOROLA
Oscillator Module (OSC)
NON-DISCLOSURE AGREEMENT REQUIRED
Figure 8-1. XTAL Oscillator External Connections
8.4.4 RC Oscillator
The RC oscillator circuit is designed for use with external R to provide a
clock source with tolerance less than 25%.
In its typical configuration, the RC oscillator requires two external
components, one R and one C. In the MC68HC908QY4, the capacitor is
internal to the chip. The R value should have a tolerance of 1% or less,
to obtain a clock source with less than 25% tolerance. The oscillator
configuration uses one component, R
EXT
.
In this configuration, the OSC2 pin can be left in the reset state as PTA4.
Or, the OSC2EN bit in the port A pullup enable register can be set to
enable the OSC2 function on the pin without affecting the clocks.
C
1
C
2
SIMOSCEN
XTALCLK
R
B
X
1
R
S
(1)
MCU
FROM SIM
OSC2OSC1
÷ 2
BUSCLKX2BUSCLKX4
TO SIMTO SIM
Note 1.
R
S
can be zero (shorted) when used with higher-frequency crystals. Refer to
manufacturer’s data. See Section 18. Electrical Specifications for component
value requirements.