xr16l2550im Exar Corporation, xr16l2550im Datasheet - Page 12

• Manufacturer Part Number: xr16l2550im
• Description: Industry Smallest Package Uart With 2.25v To 5.5v Operation
• Manufacturer: Exar Corporation

XR16L2550
LOW VOLTAGE DUART WITH 16-BYTE FIFO
The host may fill the transmit FIFO with up to 16 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
transmit empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when the FIFO and the TSR
become empty.
The receiver section contains an 8-bit Receive Shift Register (RSR) and 16 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X 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. After 8 clocks 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
F
2.12
2.11.3
IGURE
8. T
Receiver
Transmitter Operation in FIFO Mode
RANSMITTER
F
IGURE
Auto CTS Flow Control (CTS# pin)
(Xoff1/2 and Xon1/2 Reg.
Auto Software Flow Control
Flow Control Characters
16X Clock
16X Clock
7. T
O
Data
Byte
PERATION IN
RANSMITTER
Data Byte
Transmit
Transmit Shift Register (TSR)
FIFO
O
PERATION IN NON
Transmit
Register
Holding
(THR)
AND
Transm it Data Shift Register
F
LOW
Transm it
FIFO
(TSR)
12
C
ONTROL
-FIFO M
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
M
ODE
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
REV. 1.1.2