xr16l2552im Exar Corporation, xr16l2552im Datasheet - Page 23

• Manufacturer Part Number: xr16l2552im
• Description: Industry Smallest Package Uart With 2.25v To 5.5v Operation
• Manufacturer: Exar Corporation

xr
REV. 1.1.1
See “Receiver” on page 13.
See “Transmitter” on page 12.
The Baud Rate Generator (BRG) is a 16-bit counter that generates the data rate for the transmitter. The rate is
programmed through registers DLL and DLM which are only accessible when LCR bit-7 is set to ‘1’.
“Programmable Baud Rate Generator” on page 10.
The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status
and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR).
When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts
(see ISR bits 2 and 3) status will reflect the following:
A. The receive data available interrupts are issued to the host when the FIFO has reached the programmed
B. FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register
C. The receive data ready bit (LSR BIT-0) is set as soon as a character is transferred from the shift register to
4.0 INTERNAL REGISTER DESCRIPTIONS
4.1
4.2
4.3
4.4
4.4.1
A
A2-A0
DDRESS
0 1 0
1 0 0
1 0 1
1 1 0
1 1 1
trigger level. It will be cleared when the FIFO drops below the programmed trigger level.
status bit and the interrupt will be cleared when the FIFO drops below the trigger level.
the receive FIFO. It is reset when the FIFO is empty.
T
Receive Holding Register (RHR) - Read- Only
Transmit Holding Register (THR) - Write-Only
Baud Rate Generator Divisors (DLL and DLM) - Read/Write
Interrupt Enable Register (IER) - Read/Write
ABLE
IER versus Receive FIFO Interrupt Mode Operation
XOFF1 RD/WR
XOFF2 RD/WR
XON1 RD/WR
XON2 RD/WR
N
R
EFR
AME
EG
8: INTERNAL REGISTERS DESCRIPTION.
RD/WR
W
R
EAD
RITE
/
Enable
B
Auto
CTS
Bit-7
Bit-7
Bit-7
Bit-7
IT
-7
Enable
B
Auto
RTS
Bit-6
Bit-6
Bit-6
Bit-6
IT
-6
Enhanced Registers
Special
Select
B
Char
Bit-5
Bit-5
Bit-5
Bit-5
IT
-5
for more details.
23
FCR[5:4],
IER [7:4],
ISR [5:4],
MCR[7:5]
Enable
B
Bit-4
Bit-4
Bit-4
Bit-4
IT
-4
S
HADED BITS ARE ENABLED WHEN
2.25V TO 5.5V DUART WITH 16-BYTE FIFO
B
Soft-
ware
Flow
Bit-3
Bit-3
Bit-3
Bit-3
Bit-3
Cntl
IT
-3
B
ware
Soft-
Flow
Bit-2
Bit-2
Bit-2
Bit-2
Bit-2
Cntl
IT
-2
B
Soft-
ware
Flow
Bit-1
Bit-1
Bit-1
Bit-1
Bit-1
Cntl
IT
-1
B
ware
Soft-
Flow
Bit-0
Bit-0
Bit-0
Bit-0
Bit-0
Cntl
EFR B
IT
-0
IT
XR16L2552
LCR=0
-4=1
C
OMMENT
X
BF
See