User's Manual Part 2

NPort W2004 User’s Manual Installing and Configuring the Software
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lower throughput. Classical mode is recommended if you want to ensure that all data is sent
out before further processing.
FIFO
If the FIFO is Disabled, NPort W2004 will transmit one byte each time the Tx FIFO
becomes empty, and an Rx interrupt will be generated for each incoming byte. This will
result in a faster response and lower throughput. If you want to use XON/XOFF flow control,
we recommend setting the FIFO to Disable.
Fast Flush (only flushes the local buffer)
a. We have added one optional Fast Flush function to Moxa’s new NPort Real COM
driver.
b. For some applications, the user’s program will use the Win32 “PurgeComm()” function
before it reads or writes data. With our design, after the program uses this Purge Comm()
function, the NPort driver will keep querying NPort’s firmware several times to make
sure no data is queued in the NPort firmware buffer, rather than just flushing the local
buffer. This kind of design is used to satisfy some special considerations. However, it
might take more time (about several hundred milliseconds) than a native COM1,
because it needs to work via Ethernet. That’s why the native COM ports on the
motherboard can work fast with this function call, but NPort requires much more time.
In order to accommodate other applications that require a faster response time, the new
NPort driver implements a new “Fast Flush” option. Note that by default, this function
is disabled.
c. To begin with, make sure there are some “PurgeComm()” functions being used in your
application program. In this kind of situation, you might find that your NPort exhibits a
much poorer operation performance than when using the native COM1 port. Once you
have enabled the “Fast Flush” function, you can check to see if there has been an
improvement in performance.
d. By default, the optional “Fast Flush” function is disabled. If you would like to enable
this function, double click on the COM ports that are mapped to the NPort, and then
select the “Fast Flush” checkbox. You should find that when “Fast Flush” is enabled, the
NPort driver will work faster with “PurgeComm().”