FDC37B78X SMSC Corporation, FDC37B78X Datasheet - Page 76

• Manufacturer Part Number: FDC37B78X
• Description: Enhanced Super I/O Controller with ACPI Support/ Real Time Clock and Consumer IR
• Manufacturer: SMSC Corporation

This 8 bit register controls the interface with the
MODEM or data set (or device emulating a
MODEM). The contents of the MODEM control
register are described below.
Bit 0
This bit controls the Data Terminal Ready
(nDTR) output. When bit 0 is set to a logic "1",
the nDTR output is forced to a logic "0". When
bit 0 is a logic "0", the nDTR output is forced to
a logic "1".
Bit 1
This bit controls the Request To Send (nRTS)
output.
manner identical to that described above for bit
0.
Bit 2
This bit controls the Output 1 (OUT1) bit. This
bit does not have an output pin and can only be
read or written by the CPU.
Bit 3
Output 2 (OUT2). This bit is used to enable an
UART interrupt. When OUT2 is a logic "0", the
serial port interrupt output is forced to a high
impedance state - disabled. When OUT2 is a
logic "1", the serial port interrupt outputs are
enabled.
Bit 4
This bit provides the loopback feature for
diagnostic testing of the Serial Port. When bit 4
is set to logic "1", the following occur:
1. The TXD is set to the Marking State(logic
2. The
3. The output of the Transmitter Shift Register
4. All MODEM Control inputs (nCTS, nDSR,
5. The four MODEM Control outputs (nDTR,
6.
"1").
disconnected.
is "looped back" into the Receiver Shift
Register input.
nRI and nDCD) are disconnected.
nRTS, OUT1 and OUT2) are internally
connected to the four MODEM Control inputs
(nDSR, nCTS, RI, DCD).
The Modem Control output pins are forced
inactive high.
Bit 1 affects the nRTS output in a
receiver
Serial
Input
(RXD)
is
76
7. Data that is transmitted is immediately
This feature allows the processor to verify the
transmit and receive data paths of the Serial
Port. In the diagnostic mode, the receiver and
the transmitter interrupts are fully operational.
The
operational but the interrupts' sources are now
the lower four bits of the MODEM Control
Register instead of the MODEM Control inputs.
The interrupts are still controlled by the Interrupt
Enable Register.
Bits 5 through 7
These bits are permanently set to logic zero.
LINE STATUS REGISTER (LSR)
Address Offset = 5H, DLAB = X, READ/WRITE
Bit 0
Data Ready (DR).
whenever a complete incoming character has
been received and transferred into the Receiver
Buffer Register or the FIFO. Bit 0 is reset to a
logic "0" by reading all of the data in the Receive
Buffer Register or the FIFO.
Bit 1
Overrun Error (OE). Bit 1 indicates that data in
the Receiver Buffer Register was not read before
the next character was transferred into the
register,
character. In FIFO mode, an overrunn error will
occur only when the FIFO is full and the next
character has been completely received in the
shift register, the character in the shift register is
overwritten but not transferred to the FIFO. The
OE indicator is set to a logic "1" immediately
upon detection of an overrun condition, and
reset whenever the Line Status Register is read.
Bit 2
Parity Error (PE).
received data character does not have the
correct even or odd parity, as selected by the
even parity select bit. The PE is set to a logic
"1" upon detection of a parity error and is reset
to a logic "0" whenever the Line Status Register
is read.
associated with the particular character in the
received.
MODEM
thereby
In the FIFO mode this error is
Control
destroying
Bit 2 indicates that the
It is set to a logic "1"
Interrupts
the
are
previous
also