xr16v554 Exar Corporation, xr16v554 Datasheet - Page 16

• Manufacturer Part Number: xr16v554
• Description: 2.25v To 3.6v Quad Uart With 16-byte Fifo
• Manufacturer: Exar Corporation

XR16V554/554D
2.25V TO 3.6V QUAD UART WITH 16-BYTE FIFO
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 clock 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 clock rate. 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 LOW 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. See
below.
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-bit 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
2.10
2.10.1
IGURE
9. R
Receiver
Receive Holding Register (RHR) - Read-Only
ECEIVER
and Errors
16X Clock
Data Byte
Receive
O
PERATION IN NON
LSR bits
Tags in
Error
4:2
-FIFO M
Receive Data Shift
Register (RSR)
Holding Register
Receive Data
ODE
(RHR)
16
Validation
Data Bit
RHR Interrupt (ISR bit-2)
Receive Data Characters
Figure 9
RXFIFO1
and
Figure 10
REV. 1.0.2