Z8F1680SH020SG Datasheet, PDF (347/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
322
The secondary 32 K crystal oscillator mode is selected using user-programmable Flash
option bits. For information, see the Flash Option Bits section on page 276.
25.2. Main Crystal Oscillator Operation
The Flash Option bit XTLDIS controls whether the crystal oscillator is enabled during
reset. The crystal can later be disabled after reset if a new oscillator has been selected as
the system clock. If the crystal is manually enabled after reset through the OSCCTL Reg-
ister, the user code must wait at least 1000 crystal oscillator cycles for the crystal to stabi-
lize. After this period completes, the crystal oscillator can be selected as the system clock.
Figure 62 displays the recommended configuration for connection with an external funda-
mental-mode, parallel-resonant crystal operating at 20 MHz. Recommended 20 MHz crys-
tal specifications are provided in Table 172. Printed circuit board layout must add no more
than 4 pF 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
XIN
C1 = 20 pF
Crystal
XOUT
C2 = 20 pF
Figure 62. Recommended 20 MHz Crystal Oscillator Configuration
PS025015-1212
PRELIMINARY
Crystal Oscillator