XR16L784_08 Datasheet, PDF (30/51 Pages) Exar Corporation – HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART

XR16L784
HIGH PERFORMANCE 2.97V TO 5.5V QUAD UART
REV. 1.2.3
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.
4.5 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 active.
• Logic 0 = No receive FIFO reset (default).
• Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (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 active.
• Logic 0 = No transmit FIFO reset (default).
• Logic 1 = Reset the transmit FIFO pointers and FIFO level counter logic (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
This bit has no effect since TXRDY and RXRDY pins are not available in this device. It is provided for legacy
software.
• Logic 0 = Set DMA to mode 0 (default).
• Logic 1 = Set DMA to mode 1.
FCR[5:4]: Transmit FIFO Trigger Select
(logic 0 = default, TX trigger level = one)
The FCTR Bits 6-7 are associated with these 2 bits by selecting one of the four tables. The 4 user selectable
trigger levels in 4 tables are supported for compatibility reasons. These 2 bits set the trigger level for the
transmit FIFO interrupt. The UART will issue a transmit interrupt when the number of characters in the FIFO
falls below the selected trigger level, or when it gets empty in case that the FIFO did not get filled over the
trigger level on last re-load. Table 14 below shows the selections.
FCR[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
The FCTR Bits 5-4 are associated with these 2 bits. 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 14 shows the complete selections. Note that the receiver and the transmitter cannot use
different trigger tables. Whichever selection is made last applies to both the RX and TX side.
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