Contec COM-2DL-PCI, User Manual, Page: 46 / 62

4. Functions
COM-2PD(PCI)H, COM-4PD(PCI)H
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4. Functions
This section describes the functions of the board.
Communication Function
Serial Data Transmission
Sends and receives data in accordance with the RS-422A/485 standard.
The baud rate for each channel can be set independently in the range 2 to 921,600bps by software.
RS-422A/485 Control Lines
All ports include the RTS+, RTS-, CTS+, and CTS- control lines.
The lines can be controlled or monitored by software from the application
Send and Receive Data Buffers
Each channel has a separate 128-byte send and 128-byte receive buffer.
The buffers operate as FIFO buffers and help reduce the load on the CPU for high-speed
communications or system operation.
The data buffer settings (Use FIFO ON/OFF and FIFO trigger size) are set by the Device Manager
(on Windows 8, 7, Server 2008, Vista, XP, Server 2003, 2000) and by the API-TOOL configuration (on
Windows NT, Me, 98, and 95).
The FIFO trigger size specifies the data buffer size and determines the timing for generating hardware
interrupts.
Setting a large FIFO trigger size lightens the load on the CPU by reducing the number of hardware
interrupts generated by sending or receiving data.
However, as data is not actually sent or received until a certain amount of data has accumulated, the
timing at which the data reaches the opposing device is slightly delayed. Similarly, there is also a delay
in the timing between data being received and the data being passed the application.
Alternatively, setting a small FIFO trigger size or disabling FIFO operation increases the speed of data
sending and receiving but increases the load on the CPU and risks received data being missed.
As the FIFO buffer size is variable, you can adjust this setting to achieve optimum performance for your
system.