8
output pins. A checked box will output a logic high while unchecked outputs logic low. Clicking the
Check/Set Digital I/Os button or the Set Now button or the OK button will update the status of these pins.
Note: The state of each output pin will be remembered, but only if you open the same port that you used
to set the output. If you open a different port, the outputs that were last written by that port will be
displayed.
•
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
•
Rx FIFO Trigger Level
1
The Rx FIFO level generates an interrupt whenever the receive FIFO level rises above this preset trigger
level (high water mark). Raising or lowering this value can help to reduce the number of interrupts
generated by the Fastcom port during receives. This setting affects only the selected port. Modify this
value only if necessary in your application or if the receiver is generating too many interrupts for your
CPU to handle.
•
Tx FIFO Trigger Level
1
The Tx FIFO level generates an interrupt whenever the transmit FIFO level falls below this preset trigger
level (low water mark). Raising or lowering this value can help to reduce the number of interrupts
generated by the Fastcom port during transmits. This setting affects only the selected port. Modify this
value only if necessary in your application or if the transmitter is generating too many interrupts for your
CPU to handle. Tx FIFO T Tx Write Size must not exceed 64.
•
Tx Write Size
1
Tx Write Size is the number of bytes that get written to the Tx FIFO when the low water mark is reached.
Raising or lowering this value can help to reduce the number of interrupts generated by the Fastcom port
during transmits. This setting affects only the selected port. Modify this value only if necessary in your
application or if the transmitter is generating too many interrupts for your CPU to handle. Tx FIFO Trigger
+ Tx Write Size must not exceed 64.
•
Software 9-Bit Mode
Turns on or off software 9-bit mode emulation. A feature of some UARTS and microcontrollers "MCS-51
9-bit format.” If you don't know what this is, you probably do not want to use it.
•
Return 9-Bit data
Turns on or off the returning of the 9th data bit as its own character. A feature of some UARTS and
microcontrollers "MCS-51 9-bit format." If you don't know what this is, you probably do not want to use it.
•
Custom Speed
When enabled, this allows you to use a non-standard, custom baud rate inside of an application that does
not support custom rates. When this is enabled, the 9600 baud rate will be overridden with the Max Baud
rate. Just select a baud rate of 9600 in your application and you will get whatever rate you have in the
Max Baud field.
1
The results of changing the Rx FIFO Trigger, Tx FIFO Trigger, and Tx Write Size will depend entirely upon the
host PC. What lowers the number of interrupt requests on one PC will raise the number of interrupt requests on
another PC. You will have to experiment with these values to find the settings that yield the best performance
with the lowest number of interrupt requests that must be serviced by your CPU. If you do not experience
problems using the card in you PC, you should leave these at their default settings.
