XR17D154 Exar Corporation, XR17D154 Datasheet - Page 28

• Manufacturer Part Number: XR17D154
• Description: Four-channel Pci-bus Uart
• Manufacturer: Exar Corporation

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PRELIMINARY
Each UART channel provides an internal loopback capability for system diagnostic. The internal loopback
mode is enabled by setting MCR register bit-4 to logic 1. All regular UART functions operate normally.
Figure 13
output is internally routed to the receive shift register input allowing the system to receive the same data that it
was sending. The TX pin is held at logic 1 or mark condition while RTS# and DTR# are de-asserted, and
CTS#, DSR# CD# and RI# inputs are ignored.
The 4 sets of UART configuration registers are decoded using address lines A9 to A11 as shown below:
5.4
5.5
Internal Loopback
UART CHANNEL CONFIGURATION REGISTERS AND ADDRESS DECODING
shows how the modem port signals are re-configured. Transmit data from the transmit shift register
F
IGURE
13. I
NTERNAL
L
OOP
A11
0
0
0
0
B
ACK
Transmit Shif t
Receive Shif t
A10
Register
Register
0
0
1
1
A9
28
RTS#
CTS#
DTR#
DSR#
0
1
0
1
CD#
RI#
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
MC R bit-4=1
UART C
OP1#
OP2#
S
VCC
VCC
ELECTION
VCC
0
1
2
3
HANNEL
RX [3:0]
RTS# [3:0]
CTS# [3:0]
TX [3:0]
DSR# [3:0]
DTR# [3:0]
RI# [3:0]
CD# [3:0]
XR17D154
REV. P1.0.0