8
Fastcom
®
: 422/4-PCI-335
FASTCOM ASYNCPCI-335 SERIAL SETTINGS
The Serial Settings property page can be found by opening the Device Manager (Start -> Run -> devmgmt.msc ->
OK), expanding the “Ports (COM & LPT)” class and double clicking on one of the installed “Fastcom Async335
Communications Port” devices, and then clicking on the “Fastcom AsyncPCI-335 Serial Settings” tab.
Each port on the Fastcom board has all of the settings available to it. However there are two options that will
affect all other ports on that particular Fastcom board: Clock Generator Frequency and Rx Echo Cancel. All
other settings are will affect only the selected port.
Clicking on each individual setting will bring up a description of the setting in box at the top of the page. This is a
slightly more detailed version of those same descriptions.
Clock Generator Frequency
The clock generator frequency divided by the sampling rate will directly determine the maximum available
bit rate that you may use with the Fastcom board. It works like this: Windows must be able to divide the
clock frequency by the sampling rate and then by any whole number and get to your bit rate as the
answer. By default, the clock is set to 14.7456 MHz (14745600 Hz). This frequency can be divided by
whole numbers to get all of the standard bit rates (i.e. 9600, 19200, 115200, etc). Minimum = 6 MHz,
Maximum = 50 MHz.
For Example:
Frequency / Sampling rate (8 or 16) / n = bit rate
14,745,600 / 16 / 96 = 9600
This setting is global. Changing the clock generator frequency will affect all Fastcom ports on the board.
Setting the clock for one port will set it for all port of the same board.
Rx Echo Cancel
When configured to operate on a 485 network, the card’s receive and transmit lines are tied together to
make a single data line. Because of this, every time data is transmitted out of the port, it will
simultaneously be received on the same port. Enabling Rx Echo Cancel will turn off the receiver during
all transmits, eliminating this simultaneous echo. 485 transmit control must be enabled to use this
feature. This is accomplished in hardware not software; it will not affect performance.
This setting is global. Enabling or disabling this option will affect all other ports on the board.
Sampling Rate
Determines the number of times a data bit is sampled. It can be set to either 8 or 16 on a per port basis.
It is used in conjunction with clock generator frequency to determine attainable bit rates. As a general
rule, if your bit rate will be less than or equal to 3.125 Mbits/sec you should use 16 times sampling. 8
times sampling should only be used if you wish to run at bit rates over 3.125 Mbits/sec.
Max Baud
This field reads the values that you have entered in the clock generator box and the sampling box and
calculates the maximum bit rate possible using those settings. The formula used to calculate the
maximum bit rate looks like this:
Frequency / Sampling = Maximum bit rate
Or
Frequency / Sampling rate (8 or 16) / 1 = Max bit rate
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