XR16C2552 Datasheet, PDF (19/36 Pages) Exar Corporation – 2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO

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REV. 1.0.0
XR16C2552
2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO
ISR[7:6]: FIFO Enable Status
These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are
enabled.
4.6 FIFO Control Register (FCR) - Write-Only
This register is used to enable the FIFOs, clear the FIFOs, set the transmit/receive FIFO trigger levels, and
select the DMA mode. The DMA, and FIFO modes are defined as follows:
FCR[0]: TX and RX FIFO Enable
• Logic 0 = Disable the transmit and receive FIFO (default).
• Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are
written or they will not be programmed.
FCR[1]: RX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
• Logic 0 = No receive FIFO reset (default)
• Logic 1 = Reset the receive FIFO pointers (the receive shift register is not cleared or altered). This bit will
return to a logic 0 after resetting the FIFO.
FCR[2]: TX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
• Logic 0 = No transmit FIFO reset (default).
• Logic 1 = Reset the transmit FIFO pointers (the transmit shift register is not cleared or altered). This bit will
return to a logic 0 after resetting the FIFO.
FCR[3]: DMA Mode Select
Controls the behavior of the TXRDY# and RXRDY# pins. See DMA operation section for details.
• Logic 0 = Normal Operation (default).
• Logic 1 = DMA Mode.
FCR[5:4]: Reserved
FCR[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
These 2 bits are used to set the trigger level for the receive FIFO. The UART will issue a receive interrupt when
the number of the characters in the FIFO crosses the trigger level. Table 9 shows the complete selections.
TABLE 9: TRANSMIT AND RECEIVE FIFO TRIGGER LEVEL SELECTION
FCR FCR
BIT-7 BIT-6
RECEIVE
TRIGGER
LEVEL
COMPATIBILITY
0
0
1 (default) Table-A. 16C550, 16C2550, 16C2552, 16C554,
0
1
4
16C580 compatible.
1
0
8
1
1
14
4.7 Line Control Register (LCR) - Read/Write
The Line Control Register is used to specify the asynchronous data communication format. The word or
character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this
register.
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