XR17D154 Datasheet, PDF (8/69 Pages) Exar Corporation – UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART

XR17D154
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
xr
REV. 1.2.0
1.0 APPLICATION EXAMPLES
The XR17D154 is designed to operate with VCC (voltage to the UART Core Logic) greater than or equal to
VIO. See Table 1 below for valid combintions of VCC and VIO that can be used with the device..
TABLE 1: VALID COMBINATIONS OF VCC AND VIO SUPPLY VOLTAGES
VCC
VIO
5.0V
5.0V
Valid
5.0V
3.3V
Valid
3.3V
5.0V
Invalid
3.3V
3.3V
Valid
For a universal add-in card, it is usually unknown whether it will be plugged into a 3.3V or 5V PCI slot, therefore
VCC must be 5V to guarantee proper functionality in any PCI slot as shown in Figure 3. In an embedded
system, the designer can choose to use a 3.3V or 5V power supply for the UART core voltage. Of course, the
core voltage can be 3.3V only when the VIO is 3.3V. In Figure 4, examples 1-3 show valid applications of the
XR17D154 in an embedded system.
FIGURE 3. TYPICAL APPLICATION FOR A UNIVERSAL ADD-IN CARD
VIO
(3.3V or 5V)
CLK
(up to 33.34MHz)
PCI
Local
Bus
Interface
UART Core Logic
UART Channel 0
UART Channel 1
UART Channel 2
VCC = 5V
UART Channel 3
Max Crystal Frequency = 24MHz
Max External Clock = 50MHz
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