REV. 1.2.2 UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART 23 3.0 CRYSTAL OSCILLATOR / BUFFER The D154 includes an on-chip oscillator (XT" />
參數(shù)資料
型號(hào): XR17D154CV-0A-EVB
廠商: Exar Corporation
文件頁(yè)數(shù): 16/69頁(yè)
文件大?。?/td> 0K
描述: EVAL BOARD FOR XR17D154 144TQFP
標(biāo)準(zhǔn)包裝: 1
系列: *
xr
XR17D154
REV. 1.2.2
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
23
3.0 CRYSTAL OSCILLATOR / BUFFER
The D154 includes an on-chip oscillator (XTAL1 and XTAL2). The crystal oscillator provides the system clock
to the Baud Rate Generators (BRG) in each of the 4 UARTs, the 16-bit general purpose timer/counter and
internal logics. XTAL1 is the input to the oscillator or external clock buffer input with XTAL2 pin being the
output. Caution: The XTAL1 input is not 5V tolerant. See Programmable Baud Rate Generator in the UART
section for programming details.
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant with
10-22 pF capacitance load, 100ppm) connected externally between the XTAL1 and XTAL2 pins (see Figure 9).
Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal 4 baud rate generators
for standard or custom rates. However, for external clock frequencies greater than 24MHz, a 2K pull-up may be
necessary on the XTAL2 output (see Figure 10). Typically, the oscillator connections are shown in Figure 9.
For further reading on oscillator circuit please see application note DAN108 on EXAR’s web site.
FIGURE 9. TYPICAL OSCILLATOR CONNECTIONS
FIGURE 10. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE
C1
22-47pF
C2
22-47pF
14.7456
MHz
XTAL1
XTAL2
R=300K to 400K
2K
XTAL1
XTAL2
R1
VCC
External Clock
vcc
gnd
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