XR19L220_07 Datasheet, PDF (28/43 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER

XR19L220
SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER
REV. 1.0.1
LSR[7]: Receive FIFO Data Error Flag
• Logic 0 = No FIFO error (default).
• Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error
or break indication is in the FIFO data. This bit clears when there is no more error(s) in any of the bytes in the
RX FIFO.
4.10 Modem Status Register (MSR) - Read Only
This register provides the current state of the modem interface input signals. Lower four bits of this register are
used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem
changes state. These bits may be used for general purpose inputs when they are not used with modem
signals.
MSR[0]: Delta CTS Input Flag
• Logic 0 = No change on CTS input (default).
• Logic 1 = The CTS input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3).
MSR[1]: Delta DSR Input Flag
• Logic 0 = No change on DSR input (default).
• Logic 1 = The DSR input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3).
MSR[2]: Delta RI Input Flag
• Logic 0 = No change on RI input (default).
• Logic 1 = The RI input has changed from LOW to HIGH, ending of the ringing signal. A modem status
interrupt will be generated if MSR interrupt is enabled (IER bit-3).
MSR[3]: Delta CD Input Flag
• Logic 0 = No change on CD input (default).
• Logic 1 = Indicates that the CD input has changed state since the last time it was monitored. A modem status
interrupt will be generated if MSR interrupt is enabled (IER bit-3).
MSR[4]: CTS Input Status
CTS pin may function as automatic hardware flow control signal input if it is enabled and selected by Auto CTS
(EFR bit-7). Auto CTS flow control allows starting and stopping of local data transmissions based on the
modem CTS signal. A HIGH on the CTS pin will stop UART transmitter as soon as the current character has
finished transmission, and a LOW will resume data transmission. Normally MSR bit-4 bit is the complement of
the CTS input. However in the loopback mode, this bit is equivalent to the RTS bit in the MCR register. The
CTS input may be used as a general purpose input when the modem interface is not used.
MSR[5]: DSR Input Status
Normally this bit is the complement of the DSR input. In the loopback mode, this bit is equivalent to the DTR bit
in the MCR register. The DSR input may be used as a general purpose input when the modem interface is not
used.
MSR[6]: RI Input Status
Normally this bit is the complement of the RI input. In the loopback mode this bit is equivalent to bit-2 in the
MCR register. The RI input may be used as a general purpose input when the modem interface is not used.
MSR[7]: CD Input Status
Normally this bit is the complement of the CD input. In the loopback mode this bit is equivalent to bit-3 in the
MCR register. The CD input may be used as a general purpose input when the modem interface is not used.
4.11 Scratchpad Register (SPR) - Read/Write
This is a 8-bit general purpose register for the user to store temporary data. The content of this register is
preserved during sleep mode but becomes 0xFF (default) after a reset or a power off-on cycle.
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