XR16C2850 Datasheet, PDF (23/43 Pages) Exar Corporation – 3.3V AND 5V DUART WITH 128-BYTE FIFO

XR16C2850
REV. 2.0.0
3.3V AND 5V DUART WITH 128-BYTE FIFO
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FCR[3]: DMA Mode Select
Controls the behavior of the TXRDY# and RXRDY#
pins. See DMA operation section for details.
• Logic 0 = Normal Operation (default).
• Logic 1 = DMA Mode.
FCR[5:4]: Transmit FIFO Trigger Select
(logic 0 = default, TX trigger level = one)
These 2 bits set the trigger level for the transmit FIFO.
The UART will issue a transmit interrupt when the
number of characters in the FIFO falls below the se-
lected trigger level, or when it gets empty in case that
the FIFO did not get filled over the trigger level on last
re-load. Table 10 below shows the selections. EFR
bit-4 must be set to ‘1’ before these bits can be ac-
cessed. Note that the receiver and the transmitter
cannot use different trigger tables. Whichever selec-
tion is made last applies to both the RX and TX side.
FCR[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
The FCTR Bits 5-4 are associated with these 2 bits.
These 2 bits are used to set the trigger level for the
receive FIFO. The UART will issue a receive interrupt
when the number of the characters in the FIFO cross-
es the trigger level. Table 10 shows the complete se-
lections.
NOTE: The receiver and the transmitter cannot use different
trigger tables. Whichever selection is made last applies to
both the RX and TX side.
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER LEVEL SELECTION
FCTR FCTR FCR
BIT-5 BIT-4 BIT-7
FCR
BIT-6
FCR
BIT-5
FCR
RECEIVE
TRANSMIT
BIT-4 TRIGGER LEVEL TRIGGER LEVEL
COMPATIBILITY
0
0
0
0
1 (default) Table-A. 16C550, 16C2550,
0
0
1 (default)
16C2552, 16C554, 16C580
0
1
4
compatible.
1
0
8
1
1
14
0
1
0
0
0
1
1
0
1
1
0
0
8
0
1
16
1
0
24
1
1
28
16
Table-B. 16C650A compatible.
8
24
30
1
0
0
0
0
1
1
0
1
1
0
0
8
0
1
16
1
0
56
1
1
60
8
Table-C. 16C654 compatible.
16
32
56
1
1
X
X
X
X Programmable Programmable Table-D. 16C850, 16L2752,
via TRG
via TRG 16L2750, 16C2852, 16C854,
register.
register. 16C864, 16C872 compatible.
FCTR[7] = 0. FCTR[7] = 1.
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