
Advanced Notebook I/O for ISA or LPC Designs
Datasheet
SMSC SIO10N268
Page 99
Rev. 0.5 (03-24-05)
DATASHEET
is transferred from the Transmitter Holding Register into the Transmitter Shift Register. The bit is reset to logic
"0" whenever the CPU loads the Transmitter Holding Register. In the FIFO mode this bit is set when the
XMIT FIFO is empty, it is cleared when at least 1 byte is written to the XMIT FIFO. Bit 5 is a read only bit.
Bit 6
Transmitter Empty (TEMT). Bit 6 is set to a logic "1" whenever the Transmitter Holding Register (THR)
and Transmitter Shift Register (TSR) are both empty. It is reset to logic "0" whenever either the THR or
TSR contains a data character. Bit 6 is a read only bit. In the FIFO mode this bit is set whenever the THR
and TSR are both empty.
Bit 7
This bit is permanently set to logic "0" in the 450 mode. In the FIFO mode, this bit is set to a logic "1" when
there is at least one parity error, framing error or break indication in the FIFO. This bit is cleared when the
LSR is read if there are no subsequent errors in the FIFO.
8.8.1.9
Modem Status Register (MSR)
Address Offset = 6H, DLAB = X, READ/WRITE
This 8 bit register provides the current state of the control lines from the MODEM (or peripheral device). In
addition to this current state information, four bits of the MODEM Status Register (MSR) provide change
information. These bits are set to logic "1" whenever a control input from the MODEM changes state. They
are reset to logic "0" whenever the MODEM Status Register is read.
Bit 0
Delta Clear To Send (DCTS). Bit 0 indicates that the nCTS input to the chip has changed state since the last
time the MSR was read.
Bit 1
Delta Data Set Ready (DDSR). Bit 1 indicates that the nDSR input has changed state since the last time the
MSR was read.
Bit 2
Trailing Edge of Ring Indicator (TERI). Bit 2 indicates that the nRI input has changed from logic "0" to logic
"1".
Bit 3
Delta Data Carrier Detect (DDCD). Bit 3 indicates that the nDCD input to the chip has changed state.
NOTE:
Whenever bit 0, 1, 2, or 3 is set to a logic "1", a MODEM Status Interrupt is generated.
Bit 4
This bit is the complement of the Clear To Send (nCTS) input. If bit 4 of the MCR is set to logic "1", this bit is
equivalent to nRTS in the MCR.
Bit 5
This bit is the complement of the Data Set Ready (nDSR) input. If bit 4 of the MCR is set to logic "1", this bit is
equivalent to DTR in the MCR.