xr20m1170 Exar Corporation, xr20m1170 Datasheet - Page 23

• Manufacturer Part Number: xr20m1170
• Description: I2c/spi Uart With 64-byte Fifo
• Manufacturer: Exar Corporation

REV. 1.0.0
The M1170 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 19
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.
2.17
Internal Loopback
shows how the modem port signals are re-configured. Transmit data from the transmit shift register
F
IGURE
19. I
NTERNAL
L
Transmit Shift Register
Receive Shift Register
OOP
B
(RHR/FIFO)
(THR/FIFO)
ACK
RTS#
CTS#
DTR#
DSR#
CD#
RI#
23
M CR bit-4=1
VCC
OP2#
OP1#
VCC
VCC
I2C/SPI UART WITH 64-BYTE FIFO
TX
RX
RTS#
CTS#
DTR#
DSR#
RI#
CD#
XR20M1170