XR17C158 Exar Corporation, XR17C158 Datasheet - Page 31

• Manufacturer Part Number: XR17C158
• Description: Eight-channel Pci-based (UART)
• Manufacturer: Exar Corporation

XR17C158
REV. 1.0.0
The receive holding register is a 8-bit register that
holds a receive data byte from the receive shift regis-
ter (RSR). It provides the receive data interface to the
host processor. The host reads the receive data byte
on this register whenever a data byte is trasferred
from the RSR. RHR also part of the receive FIFO of
F
F
4.8 R
4.7.2 Receiver Operation with FIFO
4.8.1 Receive Holding Register (RHR)
IGURE
IGURE
Receive Data
Byte and Errors
(8XMODE Register)
16X or 8X Sampling
Clock (8XMODE Reg.)
and Errors
Data Byte
EGISTERS
16X or 8X Clock
14. R
15. R
Receive
64 bytes by 11-
bit wide FIFO
ECEIVER
ECEIVER
PCI BUS OCTAL UART
O
O
PERATION IN NON
PERATION IN
LSR bits
Flags in
Receive Data Shift
Error
Register (RSR)
4:2
Receive Data
Receive
(64-byte)
Receive Data Shift
FIFO
FIFO
Data
Register (RSR)
Holding Register
-FIFO M
Receive Data
AND
(RHR)
F
Data falls to 40
FIFO Trigger=48
Data fills to 56
Validation
LOW
Data Bit
ODE
Example:
- FIFO trigger level set at 48 bytes
- RTS/DTR hyasteresis set at +/-8 chars.
C
31
ONTROL
64 bytes by 11-bit wide, 3 extra bits are for the error
flags to be in LSR register. When the FIFO is enabled
by FCR bit-0, it acts as the first-out register of the
FIFO as new data are put over the first-in register.
The receive FIFO pointer is bumped after the RHR
register is read. Also, the error flags associated with
the data byte are immediately updated onto the line
status register (LSR) bits 1-4.
RTS#/DTR# re-asserts when data falls below
the trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.
RTS#/DTR# de-asserts when data fills above
the trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-2.
Validation
Data Bit
RHR Interrupt (ISR bit-2) is programmed
at FIFO trigger level (RXTRG).
FIFO is Enable by FCR bit-0=1
M
ODE
RHR Interrupt (ISR bit-2)
Receive Data Characters
Receive Data Characters
PRELIMINARY
RXFIFO1
RXFIFO1