XR16C872CQ EXAR [Exar Corporation], XR16C872CQ Datasheet - Page 19

• Manufacturer Part Number: XR16C872CQ
• Description: DUAL UART WITH 1284 PARALLEL PORT AND PLUG-AND-PLAY CONTROLLER
• Manufacturer: EXAR [Exar Corporation]

DSR# inputs respectively. The transmitter output (TX) and the receiver input (RX) are disconnected from their
associated interface pins, and instead are connected together internally (See Figure 7). The CTS#, DSR#, CD#,
and RI# are disconnected from their normal modem control inputs pins, and instead are connected internally to DTR#,
RTS#, OP1# and OP2#. Loopback test data enters transmit holding register via the user data bus interface, D0-D7.
The transmitter serializes the data and passes the serial data to the receive UART via the internal loopback connection.
The receive UART converts the serial data back into parallel data that is then made available at the user data interface,
D0-D7. The user optionally compares the received data to the initial transmitted data for verifying error free operation
of the UART TX/RX circuits. In this mode, the receiver, transmitter and modem control interrupts are fully operational.
However, the interrupts can only be read using lower four bits of the Modem Control Register (MCR bits 0-3) instead
of the four Modem Status Register bits 4-7. The interrupts are still controlled by the IER. Please note that OP1# and
OP2# pins are not brought out and not available.
Rev. 1.00
A E N
I O C H R D Y
R E S E T
D 0 - D 7
I O R #
I O W #
C L O C K
A 0 - A 2
E E D I O
E E C L K
E E C S
I R Q n
E E P R O M
C o n t r o l l e r
B a u d R a t e
R e g i s t e r
I n t e r r u p t
G e n e r a t o r
Select
C o n t r o l
L o g i c
L o g i c
Figure 7, Internal Loop-Back Mode Diagram
DISCONTINUED
T r a n s m i t
R e g i s t e r s
R e g i s t e r s
C o n t r o l
R e c e i v e
C o n t r o l
F I F O
F I F O
L o g i c
L o g i c
F l o w
F l o w
19
T r a n s m i t
R e g i s t e r
R e g i s t e r
R e c e i v e
S h i f t
S h i f t
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E n c o d e r
D e c o d e r
I r D A
I r D A
XR16C872
( O P 1 # )
( O P 2 # )
T X A - B
R T S # A - B
R X A - B
C D # A - B
D T R # A - B
R I # A - B
D S R # A - B
C T S # A - B