XR16L2750_05 Datasheet, PDF (13/48 Pages) Exar Corporation – 2.25V TO 5.5V DUART WITH 64-BYTE FIFO

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REV. 1.2.1
XR16L2750
2.25V TO 5.5V DUART WITH 64-BYTE FIFO
2.12.1 Receive Holding Register (RHR) - Read-Only
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 64 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.
FIGURE 9. RECEIVER OPERATION IN NON-FIFO MODE
16X or 8X Clock
(EM SR bit-7)
Receive Data Shift
Register (RSR)
Data Bit
V a lid a tio n
Receive Data Characters
R e c e iv e
Data Byte
and Errors
Error
Tags in
LSR bits
4:2
Receive Data
Holding Register
(RHR)
RHR Interrupt (ISR bit-2)
R X F IF O 1
FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
16X or 8X Clock
(EMSR bit-7)
64 bytes by 11-bit
wide
FIFO
Receive Data
Byte and Errors
Receive Data Shift
Register (RSR)
Receive
Data FIFO
Receive
Data
Data Bit
Validation
Receive Data Characters
Example
- :RX FIFO trigger level selected at 16
bytes
Data falls to
8
(See Note Below)
RTS# re-asserts when data falls below the flow
control trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
FIFO
Trigger=16
RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
Data fills to
24
RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
RXFIFO1
NOTE: Table-B selected as Trigger Table for Figure 10 (Table 10).
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