XR19L200_07 Datasheet, PDF (14/40 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER

XR19L200
SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER
REV. 1.0.1
2.15 Internal Loopback
The L200 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
including automatic hardware and software flow control. Figure 9 below shows how the internal UART 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 and RTS# pins are held
HIGH while RX and CTS# inputs are ignored. Caution: the RX input pin must be held at inactive during
loopback test else upon exiting the loopback test the UART may detect and report a false “break” signal.
FIGURE 9. INTERNAL LOOP BACK
VCC
Transmit Shift Register
TX
(THR/FIFO)
MCR bit-4=1
Receive Shift Register
(RHR/FIFO)
RX
RTS#
CTS#
DTR#
DSR#
RI#
OP1#
CD#
OP2#
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