National Instruments PCMCIA Serias, Getting Started

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Chapter 3 Configuration
PCMCIA Serial for Windows 98/95 3-4 © National Instruments Corporation
The following sections describe the advanced port setting options.
Transceiver Mode
The transceiver mode selection is available by clicking on the Advanced
button on the Port Settings tab. It shows the transceiver mode in use, and
applies only to PCMCIA-485 cards. Refer to Chapter 4, Using Your Serial
Hardware , for more information about transceiver modes.
FIFO Buffers
The FIFO buffer control is available by clicking on the Advanced button
on the Port Settings tab. FIFO buffers are present on the 16550-compatible
UARTs—one for the transmitter and one for the receiver. The receive FIFO
trigger denotes the number of characters received in the FIFO before the PC
is interrupted to read the data. The transmit FIFO trigger denotes the
maximum number of bytes written to the FIFO in a block when the PC is
interrupted to write the data. Consider the following points when selecting
FIFO settings:
• You can select larger FIFO settings to reduce the number of interrupts
and therefore minimize system overhead.
• If transfer rates are high, you can lower receive FIFO settings to
prevent overrun errors due to interrupt latency.
• If data sizes are small, selecting receive FIFO settings just above data
sizes can reduce efficiency, so select lower settings.
Note If you want your serial hardware ports to use the names
COM1
,
COM2
,
COM3
,
or
COM4
, refer to the Common Questions section of Appendix D, Troubleshooting
and Common Questions .