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Fifo Control Register
(16550 Only)
This register, which applies only to the 16550 UART, is a write-only
register located at I/O address [base+2]. It is used to enable the FIFO
mode, clear the FIFOs, set the threshold level for the receive FIFO to
generate interrupts, and to set the mode under which the device uses
DMA. Note that DMA mode is NOT supported by the QS/ES-100M.
BIT
DESCRIPTION
7
RXT1
---
Receiver FIFO Trigger Level (16550 only):
Determines the trigger level for the receiver FIFO interrupt
RXT1
RXT0
Receiver FIFO trigger level (bytes)
0
0
1
0
1
4
1
0
8
1
1
14
6
RXT0
---
5
0 --- reserved
4
0 --- reserved
3
DMAM
--- DMA mode select (16550 only):
When set (logic 1), RxRDY and TxRDY change from mode 0 to mode 1 for DMA
transfers. (DMA mode is not supported on the QS/ES-100M.)
2
XRST
--- Transmit FIFO reset (16550 only):
When set (logic 1), all bytes in the transmitter FIFO are cleared and the counter is
reset. The shift register is not cleared. XRST is self-clearing.
1
RRST
--- Receive FIFO reset (16550 only):
When set (logic 1), all bytes in the receiver FIFO are cleared and the counter is reset.
The shift register is not cleared. RRST is self-clearing.
0
FE
--- FIFO enable (16550 only):
When set (logic 1), enables transmitter and receiver FIFOs. When cleared (logic 0),
all bytes in both FIFOs are cleared. This bit must be set when other bits in the FIFO
control register are written to or the bits will be ignored.
Figure 19 --- 16550 FIFO Control Register bit definitions
18
Quatech QS-100M/ES-100M User's Manual