XR16C850CM-F Datasheet, PDF (38/56 Pages) Exar Corporation – 2.97V TO 5.5V UART WITH 128-BYTE FIFO

XR16C850
2.97V TO 5.5V UART WITH 128-BYTE FIFO
xr
REV. 2.3.1
This register is accessible when LCR = 0xBF. Note that this register is not identical to the FIFO Level Register
which is located in the general register set when FCTR bit-6 = 1.
FC[7:0]: FIFO Data Count Register
Transmit/Receive FIFO Count. Number of characters in Transmit (FCTR[7] = 1) or Receive FIFO (FCTR[7] =
0) can be read via this register.
4.18 Feature Control Register (FCTR) - Read/Write
This register controls the XR16C2850 new functions that are not available in ST16C550 or ST16C650A.
FCTR[1:0]: Auto RTS Hysteresis
User selectable RTS# hysteresis levels for hardware flow control application. After reset, these bits are set to
“0” to select the next trigger level for hardware flow control. See Table 5 for more details.
FCTR[2]: IrDa RX Inversion
• Logic 0 = Select RX input as encoded IrDa data (Idle state will be logic 0).
• Logic 1 = Select RX input as inverted encoded IrDa data (Idle state will be logic 1).
FCTR[3]: Auto RS-485 Direction Control
• Logic 0 = Standard ST16C550 mode. Transmitter generates an interrupt when transmit holding register
becomes empty and transmit shift register is shifting data out.
• Logic 1 = Enable Auto RS485 Direction Control function. The direction control signal, RS485 pin, changes
its output logic state from low to high one bit time after the last stop bit of the last character is shifted out.
Also, the Transmit interrupt generation is delayed until the transmitter shift register becomes empty. The
RS485 output pin will automatically return to a logic low when a data byte is loaded into the TX FIFO.
FCTR[5:4]: Transmit/Receive Trigger Table Select
See Table 10 for more details.
TABLE 13: TRIGGER TABLE SELECT
FCTR
BIT-5
FCTR
BIT-4
TABLE
0
0 Table-A (TX/RX)
0
1 Table-B (TX/RX)
1
0 Table-C (TX/RX)
1
1 Table-D (TX/RX)
FCTR[6]: Scratchpad Swap
• Logic 0 = Scratch Pad register is selected as general read and write register. ST16C550 compatible mode.
• Logic 1 = FIFO Count register (Read-Only), Enhanced Mode Select Register (Write-Only). Number of
characters in transmit or receive FIFO can be read via scratch pad register when this bit is set. Enhanced
Mode Select Register is selected when it is written into.
38