xr16l2552im Exar Corporation, xr16l2552im Datasheet - Page 13

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

xr
REV. 1.1.1
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
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.
The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift
Register. It provides the receive data interface to the host processor. The RHR register is part of the receive
FIFO of 16 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When
the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the
RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data
byte are immediately updated in the LSR bits 2-4
F
2.13
2.13.1
IGURE
8. T
Receiver
Receive Holding Register (RHR) - Read-Only
RANSMITTER
Auto CTS Flow Control (CTS# pin)
Auto Software Flow Control
(Xoff1/2 and Xon1/2 Reg.
Flow Control Characters
16X Clock
O
PERATION IN
Data Byte
Transmit
FIFO
AND
Transm it Data Shift Register
F
LOW
Transm it
FIFO
(TSR)
13
C
ONTROL
2.25V TO 5.5V DUART WITH 16-BYTE FIFO
M
THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
bit-0=1
empty. FIFO is Enabled by FCR
ODE
T XF IF O 1
XR16L2552