TL16C754 Datasheet, PDF (32/39 Pages) Texas Instruments – QUAD UART WITH 64-BYTE FIFO

TL16C754
QUAD UART WITH 64-BYTE FIFO
SLLS279A – OCTOBER 1998 – REVISED OCTOBER 1999
PRINCIPLES OF OPERATION
modem status register (MSR)
This 8-bit register provides information about the current state of the control lines from the modem, data set,
or peripheral device to the processor. It also indicates when a control input from the modem changes state.
Table 13 shows modem status register bit settings.
Table 13. Modem Status Register (MSR) Bit Settings
BIT NO.
BIT SETTINGS
0
Indicates that CTS input (or MCR[1] in loopback) has changed state. Cleared on a read.
1
Indicates that DSR input (or MCR[0] in loopback) has changed state. Cleared on a read.
2
Indicates that RI input (or MCR[2] in loopback) has changed state from low to high. Cleared on a read.
3
Indicates that CD input (or MCR[3] in loopback) has changed state. Cleared on a read.
4
This bit is equivalent to MCR[1] during local loop-back mode. It is the complement to the CTS input.
5
This bit is equivalent to MCR[0] during local loop-back mode. It is the complement to the DSR input.
6
This bit is equivalent to MCR[2] during local loop-back mode. It is the complement to the RI input.
7
This bit is equivalent to MCR[3] during local loop-back mode. It is the complement to the CD input.
NOTE: The primary inputs RI, CD, CTS, DSR are all active low but their registered equivalents in the MSR and MCR (in loopback) registers are
active high.
interrupt enable register (IER)
The interrupt enable register (IER) enables each of the six types of interrupt, receiver error, RHR interrupt, THR
interrupt, Xoff received, or CTS/RTS change of state from low to high. The INT output signal is activated in
response to interrupt generation. Table 14 shows interrupt enable register bit settings.
Table 14. Interrupt Enable Register (IER) Bit Settings
BIT NO.
BIT SETTINGS
0
0 = Disable the RHR interrupt
1 = Enable the RHR interrupt
1
0 = Disable the THR interrupt
1 = Enable the THR interrupt
2
0 = Disable the receiver line status interrupt
1 = Enable the receiver line status interrupt
3
0 = Disable the modem status register interrupt
1 = Enable the modem status register interrupt
4
0 = Disable sleep mode
1 = Enable sleep mode
5
0 = Disable the Xoff interrupt
1 = Enable the Xoff interrupt
6
0 = Disable the RTS interrupt
1 = Enable the RTS interrupt
7
0 = Disable the CTS interrupt
1 = Enable the CTS interrupt
NOTE: IER[7:4] can only be modified if EFR[4] is set, i.e., EFR[4] is a write enable.
Re-enabling IER[1] will not cause a new interrupt until new data has been written to the TX FIFO.
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