
XR17V358
43
REV. 1.0.6
HIGH PERFORMANCE OCTAL PCI EXPRESS UART
3.4
Internal Loopback
Each UART channel provides an internal loopback capability for system diagnostic. The internal loopback
mode
is enabled by setting MCR register bit [4] to a logic 1. All regular UART functions operate normally.
shows how the modem port signals are re-configured. Transmit data from the transmit shift register
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 HIGH or mark condition while RTS# and DTR# are de-asserted. The CTS#,
DSR#, CD# and RI# inputs are ignored.
F
IGURE
13. I
NTERNAL
L
OOP
B
ACK
TX [7:0]
RX [7:0]
Mode
m
/
Genera
l P
urpo
se
C
ontro
l
Lo
gic
In
ter
n
al
B
us
L
ines
an
d
C
ontr
o
l
S
ignal
s
RTS# [7:0]
MCR bit-4=1
VCC
VCC
VCC
Transmit Shift
Register
Receive Shift
Register
CTS# [7:0]
DTR# [7:0]
DSR# [7:0]
RI# [7:0]
CD# [7:0]
OP1#
OP2#
RTS#
CTS#
DTR#
DSR#
RI#
CD#