xr16m890 Exar Corporation, xr16m890 Datasheet - Page 14

• Manufacturer Part Number: xr16m890
• Description: Uart With 128-byte Fifo And Integrated Level Shifters
• Manufacturer: Exar Corporation

PRELIMINARY
XR16M890
UART WITH 128-BYTE FIFO AND INTEGRATED LEVEL SHIFTERS
REV. P1.1.1
1.7
Crystal Oscillator or External Clock Input
The M890 includes an on-chip oscillator to produce a clock for the baud rate generators in the device when a
crystal is connected between XTAL1 and XTAL2 as show below. The CPU data bus does not require this clock
for bus operation. The crystal oscillator provides a system clock to the Baud Rate Generators (BRGs) in the
UART. XTAL1 is the input to the oscillator or external clock buffer input with XTAL2 pin being the output. For
programming details, see
“Section 1.8, Programmable Baud Rate Generator with Fractional Divisor” on
page 15.
F
9. T
C
C
IGURE
YPICAL
RYSTAL
ONNECTIONS
XTAL1
XTAL2
R1
0-120
(Optional)
R2
500K - 1M
1.8432 MHz
Y1
to
24 MHz
C1
C2
22-47pF
22-47pF
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins. Typical oscillator connections are shown
in
Figure
9. Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal baud rate
generator for standard or custom rates. For further reading on oscillator circuit, see application note DAN108
on EXAR’s web site.
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