XR16C864
33
REV. 2.2.0
2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO
MCR[4]: Internal Loopback Enable
•
Logic 0 = Disable loopback mode (default).
•
Logic 1 = Enable local loopback mode, see loopback section and
Figure 12
.
MCR[5]: Xon-Any Enable
•
Logic 0 = Disable Xon-Any function (for 16C550 compatibility, default).
•
Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO , unless the RX character is an Xon or Xoff character and
the 864 is programmed to use the Xon/Xoff flow control.
MCR[6]: Infrared Encoder/Decoder Enable
•
Logic 0 = Enable the standard modem receive and transmit input/output interface (default).
•
Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. The TX/RX output/input are routed to the
infrared encoder/decoder. The data input and output levels conform to the IrDA infrared interface
requirement. The RX FIFO may need to be flushed upon enable. While in this mode, the infrared TX output
will be a logic 0 during idle data conditions.
MCR[7]: Clock Prescaler Select
The CLKSEL pin selects this function upon power up or reset. After the power up or reset, this register bit will
have control and can alter the logic state.
•
Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
•
Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth.
4.8 Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host. If LSR bits 1-4 are
asserted, an interrupt will be generated immediately if IER bit-2 is enabled.
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.
LSR[2]: Receive Data Parity Error Tag
•
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.
LSR[3]: Receive Data Framing Error Tag
•
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.
