XR16M570 Datasheet, PDF (10/52 Pages) Exar Corporation – 1.62V TO 3.63V HIGH PERFORMANCE UART WITH 16-BYTE FIFO

XR16M570
1.62V TO 3.63V HIGH PERFORMANCE UART WITH 16-BYTE FIFO
REV. 1.0.0
2.6 Crystal Oscillator or External Clock Input
The M570 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 2.7, Programmable Baud Rate Generator with Fractional Divisor” on
page 11.
FIGURE 6. TYPICAL CRYSTAL CONNECTIONS
XTAL1
C1
22-47pF
XTAL2
R2
500K - 1M
R1
0-120
(Optional)
Y1
1.8432 MHz
to
24 MHz
C2
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 6. Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal baud rate
generator for standard or custom rates. The BGA package has XTAL1 only, the external clock is required. For
further reading on oscillator circuit, see application note DAN108 on EXAR’s web site.
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