XR16L2551_07 Datasheet, PDF (11/49 Pages) Exar Corporation – LOW VOLTAGE DUART WITH POWERSAVE

REV. 1.1.3
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS
XTAL1
XTAL2
R2
500 KΩ - 1 MΩ
R1
0-120 Ω
(Optional)
C1
22-47 pF
Y1
1.8432 MHz
to
24 MHz
C2
22-47 pF
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 100 ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4), with an external 500 kΩ
to 1 MΩ resistor across it. Alternatively, an external clock can be connected to the XTAL1 pin to clock the
internal baud rate generator for standard or custom rates. Typical oscillator connections are shown in Figure 4.
For further reading on oscillator circuit please see application note DAN108 on EXAR’s web site.
2.9 Programmable Baud Rate Generator
A single baud rate generator is provided for the transmitter and receiver, allowing independent TX/RX channel
control. The programmable Baud Rate Generator is capable of operating with a crystal frequency of up to 24
MHz. However, with an external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2 pin (as
shown in Figure 5) it can extend its operation up to 50 MHz (3.125Mbps serial data rate) at room temperature
and 5.0V.
FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE
External Clock
vcc
gnd
VCC
R1
2K
XTAL1
XTAL2
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