RC56D, RC336D, and RC144D Modem Device Sets Designer’s Guide
4-4
Conexant
1154
4.2.2 FCR - FIFO Control Register (Addr = 2, Write Only)
The FCR is a write-only register used to enable FIFO mode, clear the RX FIFO and TX FIFO, enable DMA mode, and set the
RX FIFO trigger level.
Bits 7-6
RX FIFO Trigger Level.
FCR7 and FCR6 set the trigger level for the RX FIFO (Receiver Data Available) interrupt.
FCR7
FCR6
RX FIFO Trigger Level (Bytes)
0
0
01
0
1
04
1
0
08
1
1
14
Bits 5-4
Not used.
Bit 3
DMA Mode Select.
When FIFO mode is selected (FCR0 = 1), FCR3 selects non-DMA operation (FCR3 = 0) or DMA operation
(FCR3 = 1). When FIFO mode is not selected (FCR0 = 0), this bit is not used (the modem operates in non-
DMA mode in 16450 operation).
DMA operation in FIFO mode.
RXRDY will be asserted when the number of characters in the RX FIFO is equal to or greater than the value in
the RX FIFO Trigger Level (IIR0-IIR3 = 4h) or the received character timeout (IIR0-IIR3 = Ch) has occurred.
RXRDY will go inactive when there are no more characters in the RX FIFO.
TXRDY will be asserted when there are one or more empty (unfilled) locations in the TX FIFO. TXRDY will go
inactive when the TX FIFO is completely full.
Non-DMA operation in FIFO mode.
RXRDY will be asserted when there are one or more characters in the RX FIFO. RXRDY will go inactive when
there are no more characters in the RX FIFO.
TXRDY will be asserted when there are no characters in the TX FIFO. TXRDY will go inactive when the first
character is loaded into the TX FIFO Buffer.
Bit 2
TX FIFO Reset.
When FCR2 is a 1, all bytes in the TX FIFO are cleared. This bit is cleared automatically by the modem.
Bit 1
RX FIFO Reset.
When FCR1 is a 1, all bytes in the RX FIFO are cleared. This bit is cleared automatically by the modem.
Bit 0
FIFO Enable.
When FCR0 is a 0, 16450 mode is selected and all bits are cleared in both FIFOs. When FCR0 is a 1, FIFO
mode (16550A mode) is selected and both FIFOs are enabled. FCR0 must be a 1 when other bits in the FCR
are written or they will not be acted upon.
Summary of Contents for RC144D
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