
XR16C854/XR16C854D
3.3V AND 5V QUAD UART WITH 128-BYTE FIFO
REV. 2.0
á
24
4.0
4.1
INTERNAL REGISTER DESCRIPTIONS
R
ECEIVE
H
OLDING
R
EGISTER
(RHR) - R
EAD
-
O
NLY
See “Receiver” on page 15..
4.2
T
RANSMIT
H
OLDING
R
EGISTER
(THR) - W
RITE
-
O
NLY
See “Transmitter” on page 14..
4.3
I
NTERRUPT
E
NABLE
R
EGISTER
(IER) - R
EAD
/
W
RITE
The Interrupt Enable Register (IER) masks the inter-
rupts from receive data ready, transmit empty, line
status and modem status registers. These interrupts
are reported in the Interrupt Status Register (ISR).
4.3.1
IER versus Receive FIFO Interrupt Mode
Operation
When the receive FIFO (FCR BIT-0 = 1) and receive
interrupts (IER BIT-0 = 1) are enabled, the RHR inter-
rupts (see ISR bits 2 and 3) status will reflect the fol-
lowing:
A.
The receive data available interrupts are issued
to the host when the FIFO has reached the pro-
grammed trigger level. It will be cleared when the
FIFO drops below the programmed trigger level.
Baud Rate Generator Divisor
0 0 0
DLL
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7] = 1
LCR
≠
0xBF
0 0 1
DLM
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
0 0 0
DREV
RD
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7] = 1
LCR
≠
0xBF
DLL=0x00
DLM=0x00
0 0 1
DVID
RD
0
0
0
1
0
1
0
0
Enhanced Registers
0 0 0
TRG
WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR=0
X
BF
0 0 0
FC
RD
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
0 0 1
FCTR
RD/WR
RX/TX
Mode
SCPAD
Swap
Trig
Table
Bit-1
Trig
Table
Bit-0
Auto
RS485
Direction
Control
RX IR
Input
Inv.
Auto
RTS
Hyst
Bit-1
Auto
RTS
Hyst
Bit-0
0 1 0
EFR
RD/WR
Auto
CTS#
Enable
Auto
RTS#
Enable
Special
Char
Select
Enable
IER [7:4],
ISR [5:4],
FCR[5:4],
MCR[7:5]
Soft-
ware
Flow
Cntl
Bit-3
Soft-
ware
Flow
Cntl
Bit-2
Soft-
ware
Flow
Cntl
Bit-1
Soft-
ware
Flow
Cntl
Bit-0
1 0 0
XON1
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1 0 1
XON2
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1 1 0
XOFF1 RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1 1 1
XOFF2 RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
X X X
FSTAT
RD
RX-
RDYD#
RX-
RDYC#
RX-
RDYB#
RX-
RDYA#
TX-
RDYD#
TX-
RDYC#
TX-
RDYB#
TX-
RDYA#
FSRS# pin is
a logic 0. No
address lines
required.
T
ABLE
9: INTERNAL REGISTERS DESCRIPTION.
S
HADED
BITS
ARE
ENABLED
WHEN
EFR B
IT
-4=1
A
DDRESS
A2-A0
R
EG
N
AME
R
EAD
/
W
RITE
B
IT
-7
B
IT
-6
B
IT
-5
B
IT
-4
B
IT
-3
B
IT
-2
B
IT
-1
B
IT
-0
C
OMMENT