XR19L400_09 Datasheet, PDF (19/46 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER

XR19L400
REV. 1.0.3
SINGLE CHANNEL INTEGRATED UART AND RS-485 TRANSCEIVER
2.13 Internal Loopback
The L400 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 11 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.
FIGURE 11. INTERNAL LOOP BACK
Transmit Shift Register
(THR/FIFO)
VCC
MCR bit-4=1
Receive Shift Register
(RHR/FIFO)
VCC
RTS
CTS
VCC
DTR
DSR
RI
OP1#
OP2#
CD
TX
RX
RTS#
CTS#
DTR#
DSR#
RI#
CD#
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