XR17D154IV Exar Corporation, XR17D154IV Datasheet - Page 23

• Manufacturer Part Number: XR17D154IV
• Description: Universal QUART W/ PCI Bus Interface.
• Manufacturer: Exar Corporation

Specifications of XR17D154IV

• Features: *
• Number Of Channels: 4, QUART
• Fifo's: 64 Byte
• Protocol: RS485
• Voltage - Supply: 3.3V, 5V
• With Auto Flow Control: Yes
• With Irda Encoder/decoder: Yes
• With False Start Bit Detection: Yes
• With Modem Control: Yes
• Mounting Type: Surface Mount
• Package / Case: 144-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS Compliant

xr
REV. 1.2.2
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
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
For further reading on oscillator circuit please see application note DAN108 on EXAR’s web site.
3.0 CRYSTAL OSCILLATOR / BUFFER
F
IGURE
F
IGURE
9. T
vcc
gnd
Figure
YPICAL OSCILLATOR CONNECTIONS
10. E
22-47pF
XTAL1
External Clock
C1
10). Typically, the oscillator connections are shown in
R=300K to 400K
XTERNAL
R1
2K
14.7456
VCC
MHz
23
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
C
LOCK
22-47pF
XTAL2
XTAL1
XTAL2
C2
C
ONNECTION FOR
E
XTENDED
D
ATA
XR17D154
R
Figure
ATE
Figure
9).
9.