xr17c152im Exar Corporation, xr17c152im Datasheet - Page 20

• Manufacturer Part Number: xr17c152im
• Description: 5v Pci Bus Dual Uart
• Manufacturer: Exar Corporation

XR17C152
5V PCI BUS DUAL UART
The 152 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 2 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. 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
Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal 2 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
further reading on oscillator circuit please see application note DAN108 on EXAR’s web site.
2.0 CRYSTAL OSCILLATOR / BUFFER
F
IGURE
F
IGURE
7. T
vcc
gnd
Figure
YPICAL OSCILLATOR CONNECTIONS
8. E
2 2 -4 7 pF
X T A L1
External Clock
C 1
XTERNAL
8). Typical oscillator connections are shown in
R =3 0 0 K to 4 00 K
R1
2K
1 4 .7 45 6
VCC
M H z
20
C
LOCK
2 2 -4 7 pF
X T A L2
XTAL1
XTAL2
C 2
C
ONNECTION FOR
E
XTENDED
D
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ATA
Figure
R
ATE
REV. 1.2.0
Figure
7. For
7).