xr16m2550 Exar Corporation, xr16m2550 Datasheet - Page 20

• Manufacturer Part Number: xr16m2550
• Description: High Performance Low Voltage Duart With 16-byte Fifo
• Manufacturer: Exar Corporation

XR16M2550
HIGH PERFORMANCE LOW VOLTAGE DUART WITH 16-BYTE FIFO
The M2550 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
output is internally routed to the receive shift register input allowing the system to receive the same data that it
was sending. The TX, RTS# and DTR# pins are held while the CTS#, DSR#, CD# and RI# inputs are ignored.
Caution: the RX input pin must be held HIGH during loopback test,+ else upon exiting the loopback test the
UART may detect and report a false “break” signal. Also, auto RTS/CTS flow control 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
12. 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
20
VCC
VCC
OP1#
VCC
A
VCC
AND
B
TXA/TXB
RXA/RXB
RTSA#/RTSB#
CTSA#/CTSB#
DTRA#/DTRB#
DSRA#/DSRB#
RIA#/RIB#
CDA#/CDB#
OP2A#/OP2B#
REV. 1.0.2