XR17C158 Exar Corporation, XR17C158 Datasheet - Page 36

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

PRELIMINARY
2=0. If the modem interface is not used, this output
may be used for general purpose.
• Logic 0 = Force RTS# output to a logic 1. (default)
• Logic 1 = Force RTS# output to a logic 0.
MCR[2]: DTR# or RTS# for Auto Flow Control
DTR# or RTS# auto hardware flow control select.
This bit is in effect only when auto RTS/DTR is en-
abled by EFR bit-6.
• Logic 0 = RTS# pin is used for auto hardware flow
• Logic 1 = DTR# pin is used for auto hardware flow
MCR[3]:
Reserved. Logic zero is default.
MCR[4]: Internal Loopback Enable
• Logic 0 = Disable loopback mode. (default)
• Logic 1 = Enable local loopback mode, see loop-
MCR[5]: Xon-Any Enable
• Logic 0 = Disable Xon-Any function (for 16C550
• Logic 1 = Enable Xon-Any function. In this mode
MCR[6]: Infrared Encoder/Decoder Enable
• Logic 0 = Enable the standard modem receive and
• Logic 1 = Enable infrared IrDA receive and transmit
MCR[7]: Clock Prescaler Select
• Logic 0 = Divide by one. The input clock from the
• Logic 1 = Divide by four. The prescaler divides the
Line Status Register (LSR)
control.
control.
back section and
compatibility). (default).
any RX character received will enable Xon, resume
data transmission.
transmit input/output interface. (default)
inputs/outputs. While in this mode, the TX/RX out-
put/input are routed to the infrared encoder/
decoder. The data input and output levels will con-
form to the IrDA infrared interface requirement. As
such, while in this mode the infrared TX output will
be a logic 0 during idle data conditions. FCTR bit-4
may be selected to invert the RX input signal level
going to the decoder for infrared modules that pro-
vide rather an inverted output.
crystal or external clock is fed directly to the Pro-
grammable Baud Rate Generator without further
modification, i.e., divide by one. (default).
input clock from the crystal or external clock by four
and feeds it to the Programmable Baud Rate Gen-
erator, hence, data rates become one forth.
Figure
11.
36
This register provides the status of data transfers be-
tween the UART and the host.
LSR[0]: Receive Data Ready Indicator
• Logic 0 = No data in receive holding register or
• Logic 1 = Data has been received and is saved in
LSR[1]: Receiver Overrun Flag
• Logic 0 = No overrun error. (default)
• Logic 1 = Overrun error. A data overrun error condi-
LSR[2]: Receive Data Parity Error Flag
• Logic 0 = No parity error. (default)
• Logic 1 = Parity error. The receive character in
LSR[3]: Receive Data Framing Error Flag
• Logic 0 = No framing error. (default)
• Logic 1 = Framing error. The receive character did
LSR[4]: Receive Break Flag
• Logic 0 = No break condition. (default)
• Logic 1 = The receiver received a break signal (RX
LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register Empty indi-
cator. This bit indicates that the transmitter is ready to
accept a new character for transmission. In addition,
this bit causes the UART to issue an interrupt to the
host when the THR interrupt enable is set. The THR
bit is set to a logic 1 when the last data byte is trans-
ferred from the transmit holding register to the trans-
mit shift register. The bit is reset to logic 0 concurrent-
ly with the data loading to the transmit holding regis-
ter by the host. In the FIFO mode this bit is set when
the transmit FIFO is empty; it is cleared when at least
1 byte is written to the transmit FIFO.
LSR[6]: Transmit Shift Register Empty Flag
FIFO. (default).
the receive holding register or FIFO.
tion occurred in the receive shift register. This hap-
pens when additional data arrives while the FIFO is
full. In this case the previous data in the receive
shift register is overwritten. Note that under this
condition the data byte in the receive shift register
is not transferred into the FIFO, therefore the data
in the FIFO is not corrupted by the error.
RHR does not have correct parity information and
is suspect. This error is associated with the char-
acter available for reading in RHR.
not have a valid stop bit(s). This error is associated
with the character available for reading in RHR.
was a logic 0 for one character frame time). In the
FIFO mode, only one break character is loaded into
the FIFO. The break indication remains until the RX
input returns to the idle condition, “mark” or logic 1.
PCI BUS OCTAL UART
XR17C158
REV. 1.0.0