xr16v554 Exar Corporation, xr16v554 Datasheet - Page 27

• Manufacturer Part Number: xr16v554
• Description: 2.25v To 3.6v Quad Uart With 16-byte Fifo
• Manufacturer: Exar Corporation

REV. 1.0.2
LSR[4]: Receive Break Tag
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LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register Empty indicator. The THR bit is set to a logic 1 when the last data byte
is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0
concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set
when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte.
LSR[6]: THR and TSR Empty Flag
This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or
TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and
transmit shift register are both empty.
LSR[7]: Receive FIFO Data Error Flag
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This register is writeable but it is not recommended. The MSR 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
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MSR[1]: Delta DSR# Input Flag
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MSR[2]: Delta RI# Input Flag
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MSR[3]: Delta CD# Input Flag
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4.9
Logic 0 = No break condition (default).
Logic 1 = The receiver received a break signal (RX was LOW for at least 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 HIGH.
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.
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).
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).
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).
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).
Modem Status Register (MSR) - Read/Write
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2.25V TO 3.6V QUAD UART WITH 16-BYTE FIFO
XR16V554/554D