XR16C864 View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XR16C864' PDF : 51 Pages View PDF
XR16C864
2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO
REV. 2.2.0
2.22 Internal Loopback
The 864 UART provides an internal loopback capability for system diagnostic purposes. The internal loopback
mode is enabled by setting MCR register bit-4 to 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 logic 1 or mark condition while RTS# and DTR# are de-asserted, and
CTS#, DSR# CD# and RI# inputs are ignored. Caution: the RX input must be held to a logic 1 during loopback
test else upon exiting the loopback test the UART may detect and report a false “break” signal.
FIGURE 12. INTERNAL LOOP BACK IN CHANNELS A-D
Transmit Shift Register
(THR/FIFO)
VCC
MCR bit-4=1
Receive Shift Register
(RHR/FIFO)
VCC
RTS#
CTS#
VCC
DTR#
DSR#
VCC
OP1#
RI#
VCC
OP2#
CD#
TX A-D
RX A-D
RTS# A-D
CTS# A-D
DTR# A-D
DSR# A-D
OP1# A-D/RS485
RI# A-D
OP2# A-D
CD# A-D
22
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