xr16l2550im Exar Corporation, xr16l2550im Datasheet - Page 19

• Manufacturer Part Number: xr16l2550im
• Description: Industry Smallest Package Uart With 2.25v To 5.5v Operation
• Manufacturer: Exar Corporation

REV. 1.1.2
The L2550 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 13
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 pins 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. Also,
Auto RTS/CTS is not supported during internal loopback.
2.19
Internal Loopback
shows how the modem port signals are re-configured. Transmit data from the transmit shift register
F
IGURE
13. I
NTERNAL
Transmit Shift Register
Receive Shift Register
L
OOP
(RHR/FIFO)
(THR/FIFO)
B
ACK IN
C
RTS#
CTS#
DTR#
DSR#
OP2#
CD#
RI#
HANNEL
MCR bit-4=1
19
VCC
OP1#
VCC
VCC
A
VCC
AND
LOW VOLTAGE DUART WITH 16-BYTE FIFO
B
TXA/TXB
RXA/RXB
RTSA#/RTSB#
CTSA#/CTSB#
DTRA#/DTRB#
DSRA#/DSRB#
RIA#/RIB#
CDA#/CDB#
OP2A#/OP2B#
XR16L2550