B&B Electronics 3PCIOU4 - Manual - Manual (Page 21)

Setting Driver Options
Document Number 3PCI-0712m Chapter 4 15
Figure 8. Advanced Port Settings
Setting the FIFO Buffers
MIport cards use UARTs that contain 64-byte transmit and receive FIFO (first in, first
out) buffer registers. The transmit buffer holds the data to be sent; the receive buffer
holds the data received.
The Transmit buffer: Low parameter in the Advanced Port Settings dialog allows you
to set the minimum value at which the UART will request more data from the computer.
As the MIport card is transmitting data, the number of bytes left in the transmit buffer will
decrease. When the buffer reaches the value set, the UART will request more data from
program memory. This is intended to optimize the throughput of the data. Typically this
parameter is set at zero and usually does not have to be changed.
The Receive buffer: Low parameter in the Advance Port Settings dialog allows you to
set the value at which the UART will request that the computer read the data that has
been received. As the MIport card is receiving data the contents of the receive buffer
increases, when it reaches the value set, the UART will request that the computer
transfer the contents of the buffer to program memory. This is intended to optimize the
throughput of the data. The default value is 14. Usually this parameter does not have to
be changed.
Setting the RTS Control Parameter
1. Set RTS Control to Normal for RS-232; set RTS Control to RS-485 Mode
for 2-wire or 4-wire RS-485 operation. Either setting can be used for RS-422.
Typically the COM parameters set in this dialog box are overridden by the
software application.