
XR17V252
39
REV. 1.0.2
66 MHZ PCI BUS DUAL UART WITH POWER MANAGEMENT SUPPORT
4.7.2
Receiver Operation with FIFO
5.0
UART CONFIGURATION REGISTERS
5.1
Receive Holding Register (RHR) - Read only
5.2
Transmit Holding Register (THR) - Write only
5.3
Baud Rate Generator Divisors (DLM, DLL and DLD)
The Baud Rate Generator (BRG) generates the data rate for the transmitter and receiver. The rate is
programmed through registers DLM, DLL and DLD which are only accessible when LCR bit [7] is set to logic 1.
details.
5.4
Interrupt Enable Register (IER) - Read/Write
The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status
and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR) and also
encoded in INT (INT0-INT3) register in the Device Configuration Registers.
5.4.1
IER versus Receive FIFO Interrupt Mode Operation
When the receive FIFO (FCR bit [0] = a logic 1) and receive interrupts (IER bit [0] = logic 1) are enabled, the
RHR interrupts (see ISR bits [4:3]) status will reflect the following:
A.
The receive data available interrupts are issued to the host when the FIFO has reached the programmed
trigger level. It will be cleared when the FIFO drops below the programmed trigger level.
B.
FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register
status bit and the interrupt will be cleared when the FIFO drops below the trigger level.
C.
The receive data ready bit (LSR bit [0]) is set as soon as a character is transferred from the shift register to
the receive FIFO. It is reset when the FIFO is empty.
FIGURE 18. RECEIVER OPERATION IN FIFO AND FLOW CONTROL MODE
Receive Data Shift
Register (RSR)
RXFIFO1
16X or 8X Sampling
Clock (8XMODE Reg.)
E
rror
Fl
ag
s
(64-s
ets)
E
rro
rFl
ags
i
n
LS
R
bi
ts
4:2
64 bytes by 11-
bit wide FIFO
Receive Data Characters
FIFO Trigger=48
Example:
- FIFO trigger level set at 48 bytes
- RTS/DTR hyasteresis set at +/-8 chars.
Data fills to 56
Data falls to 40
Data Bit
Validation
Receive Data
FIFO
(64-byte)
Receive
Data
Receive Data
Byte and Errors
RHR Interrupt (ISR bit-2) is programmed
at FIFO trigger level (RXTRG).
FIFO is Enable by FCR bit-0=1
RTS#/DTR# de-asserts when data fills above
the trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.
RTS#/DTR# re-asserts when data falls below
the trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.