xr16m780 Exar Corporation, xr16m780 Datasheet - Page 24

• Manufacturer Part Number: xr16m780
• Description: 1.62v To 3.63v High Performance Uart With 64-byte Fifo
• Manufacturer: Exar Corporation

XR16M780
1.62V TO 3.63V HIGH PERFORMANCE UART WITH 64-BYTE FIFO
The M780 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.
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 HIGH 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 HIGH during loopback
test else upon exiting the loopback test the UART may detect and report a false “break” signal.
F
2.18
IGURE
15. I
Internal Loopback
Figure 15
NTERNAL
shows how the modem port signals are re-configured. Transmit data from the transmit shift
L
OOPBACK
T ra n s m it S h ift R e g is te r
R e c e iv e S h ift R e g is te r
(R H R /F IF O )
(T H R /F IF O )
24
R T S #
C T S #
D T R #
D S R #
C D #
R I#
M C R b it-4 = 1
V C C
O P 2 #
O P 1 #
V C C
V C C
T X
R X
R T S #
C T S #
D T R #
D S R #
R I#
C D #
REV. 1.0.0