XR17V358 Datasheet, PDF (41/68 Pages) Exar Corporation – HIGH PERFORMANCE OCTAL PCI EXPRESS UART

PRELIMINARY
XR17V358
REV. P1.0.2
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.
Figure 12 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.
FIGURE 12. INTERNAL LOOP BACK
VCC
Transm it Shift
R e g is te r
M CR bit-4=1
Receive Shift
R e g is te r
VCC
RTS#
CTS#
DTR#
VCC
DSR#
R I#
CD#
OP1#
OP2#
TX [7:0]
RX [7:0]
RTS# [7:0]
CTS# [7:0]
DTR# [7:0]
DSR# [7:0]
RI# [7:0]
CD# [7:0]
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