xr16l2750im Exar Corporation, xr16l2750im Datasheet - Page 12

• Manufacturer Part Number: xr16l2750im
• Description: High-performance 2.25v - 5.5v Duart
• Manufacturer: Exar Corporation

XR16L2750
2.25V TO 5.5V DUART WITH 64-BYTE FIFO
The host may fill the transmit FIFO with up to 64 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the
amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by
IER bit-1. The TSR flag (LSR bit-6) is set when TSR/FIFO becomes empty.
The receiver section contains an 8-bit Receive Shift Register (RSR) and 64 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X/8X clock (EMSR bit-7) for timing. It verifies
and validates every bit on the incoming character in the middle of each data bit. On the falling edge of a start or
false start bit, an internal receiver counter starts counting at the 16X/8X clock rate. After 8 clocks (or 4 if 8X) the
start bit period should be at the center of the start bit. At this time the start bit is sampled and if it is still a logic
0 it is validated. Evaluating the start bit in this manner prevents the receiver from assembling a false character.
The rest of the data bits and stop bits are sampled and validated in this same manner to prevent false framing.
If there were any error(s), they are reported in the LSR register bits 2-4. Upon unloading the receive data byte
from RHR, the receive FIFO pointer is bumped and the error tags are immediately updated to reflect the status
of the data byte in RHR register. RHR can generate a receive data ready interrupt upon receiving a character
or delay until it reaches the FIFO trigger level. Furthermore, data delivery to the host is guaranteed by a
receive data ready time-out interrupt when data is not received for 4 word lengths as defined by LCR[1,0] plus
12 bits time. This is equivalent to 3.7-4.6 character times. The RHR interrupt is enabled by IER bit-0.
F
F
2.12
2.11.3
IGURE
IGURE
7. T
8. T
Receiver
Transmitter Operation in FIFO Mode
RANSMITTER
RANSMITTER
Auto CTS Flow Control (CTS# pin)
(Xoff1/2 and Xon1/2 Reg.
Auto Software Flow Control
Flow Control Characters
16X or 8X Clock
(EMSR bit-7)
(EMSR Bit-7)
O
O
16X or 8X
PERATION IN NON
PERATION IN
Clock
Data
Byte
Data Byte
Transmit
Transmit Shift Register (TSR)
FIFO
-FIFO M
AND
Transmit
Register
Holding
Transm it Data Shift Register
(THR)
F
LOW
ODE
Transm it
FIFO
(TSR)
12
C
ONTROL
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
M
THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
empty. FIFO is Enabled by FCR
bit-0=1
ODE
M
S
B
TXNOFIFO1
L
S
B
T XF IF O 1
xr
REV. 1.2.1