Z8FMC16100 Series Flash MCU
Product Specification
237
On-Chip Oscillator
The products in the Z8FMC16100 Series Flash MCU features an on-chip oscillator for use
with external crystals with frequencies ranging from 32KHz to 20MHz. In addition, the
oscillator can support ceramic resonators with oscillation frequencies up to 20MHz. This
oscillator generates the primary system clock for the internal eZ8 CPU and the majority of
the on-chip peripherals. Alternatively, the XIN input pin can also accept a CMOS-level
clock input signal (32KHz–20MHz). If an external clock generator is used, the XOUT pin
must remain unconnected.
When configured for use with crystal oscillators or external clock drivers, the frequency of
the signal on the XIN input pin determines the frequency of the system clock (that is, no
internal clock divider).
Crystal Oscillator Operation
Figure 40 illustrates a recommended configuration for connection with an external funda-
mental-mode, parallel-resonant crystal operating at 20MHz. Recommended 20MHz crys-
tal specifications are provided in Table 132. The printed circuit board layout must add no
more than 4pF of stray capacitance to either the XIN or XOUT pins. If oscillation does not
occur, reduce the values of capacitors C1 and C2 to decrease loading.
On-Chip Oscillator
XIN
XOUT
20 MHz Crystal
(Fundamental Mode)
C2= 22 pF
C2 = 22 pF
Figure 40. Recommended 20MHz Crystal Oscillator Configuration
PS024604-1005
P R E L I M I N A R Y
Crystal Oscillator Operation
ZILOG [ ZILOG, INC. ]
