XR16C2550 Datasheet, PDF (22/38 Pages) Exar Corporation – 2.97V TO 5.5V DUART WITH 16-BYTE FIFO

XR16C2550
2.97V TO 5.5V DUART WITH 16-BYTE FIFO
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REV. 1.0.1
MCR[3]: OP2# Output / INT Output Enable
This bit enables and disables the operation of INT, interrupt output. If INT output is not used, OP2# can be
used as a general purpose output.
• Logic 0 = INT (A-B) outputs disabled (three state mode) and OP2# output set to a logic 1 (default).
• Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output set to a logic 0.
MCR[4]: Internal Loopback Enable
• Logic 0 = Disable loopback mode (default).
• Logic 1 = Enable local loopback mode, see loopback section and Figure 11.
MCR[7:5]: Reserved
4.8 Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host.
LSR[0]: Receive Data Ready Indicator
• Logic 0 = No data in receive holding register or FIFO (default).
• Logic 1 = Data has been received and is saved in the receive holding register or FIFO.
LSR[1]: Receiver Overrun Flag
• Logic 0 = No overrun error (default).
• Logic 1 = Overrun error. A data overrun error condition occurred in the receive shift register. This happens
when additional data arrives while the FIFO is full. In this case the previous data in the receive shift register
is overwritten. Note that under this condition the data byte in the receive shift register is not transferred into
the FIFO, therefore the data in the FIFO is not corrupted by the error. An interrupt will be generated
immediately if LSR interrupt is enabled (IER bit-2).
LSR[2]: Receive Data Parity Error Flag
• Logic 0 = No parity error (default).
• Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect.
This error is associated with the character available for reading in RHR. If the LSR interrupt is enabled (IER
bit-2), an interrupt will be generated when the character is in the RHR.
LSR[3]: Receive Data Framing Error Flag
• Logic 0 = No framing error (default).
• Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with
the character available for reading in RHR. If the LSR interrupt is enabled (IER bit-2), an interrupt will be
generated when the character is in the RHR.
LSR[4]: Receive Break Flag
• Logic 0 = No break condition (default).
• Logic 1 = The receiver received a break signal (RX was a logic 0 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 logic 1. If the LSR interrupt is enabled (IER bit-2), an interrupt will
be generated when the character is in the RHR.
LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register Empty indicator. This bit indicates that the transmitter is ready to
accept a new character for transmission. In addition, this bit causes the UART to issue an interrupt to the host
when the THR interrupt enable is set. 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.
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