EZ80L92MCU Datasheet, PDF (213/241 Pages) Zilog, Inc. – eZ80Acclaim Flash Microcontrollers

eZ80L92 MCU
Product Specification
198
On-Chip Oscillators
The eZ80L92 MCU features two on-chip oscillators for use with an external crystal. The
primary oscillator generates the system clock for the internal CPU and the majority of the
on-chip peripherals. Alternatively, the X_IN input pin can also accept a CMOS-level clock
input signal. If an external clock generator is used, the X_OUT pin should be left uncon-
nected. The secondary oscillator can drive a 32 KHz crystal to generate the time-base for
the Real-Time Clock.
20 MHz Primary Crystal Oscillator Operation
Figure 44 illustrates a recommended configuration for connection with an external
20MHz, fundamental-mode, parallel-resonant crystal. Recommended crystal specifica-
tions are provided in Table 125. Resistor R₁ limits total power dissipation by the crystal.
Printed circuit board layout should add no more than 4pF of stray capacitance to either the
X_IN or X_OUT pins. If oscillation does not occur, reduce the values of capacitors C₁ and C₂
to decrease loading.
On-Chip Oscillator
X_IN
20 MHz Crystal
(Fundamental Mode)
X_OUT
R₁ = 220 Ω
C₂ = 22 pF
R₂ = 100 KΩ
C₂ = 22 pF
Figure 44. Recommended Crystal Oscillator Configuration (20MHz operation)
PS013012-1004
PRELIMINARY
On-Chip Oscillators