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4. You can select “Data Rate” change the crystal Frequency of input clock.
This page provides a list of common crystal values used with COM ports. Select “Detect crystal
frequency” to detect the input clock frequency to the UART. (This requires that the port is not currently in
use by another application).
The baud rate can optionally be adjusted according to the data rate required. To enable the advanced
baud rate configuration options, deselect the “Use default baud rate” box. In normal operation, the driver
will generate the desired baud rate from the crystal frequency. The quad speed option will multiply all
application selected baud rates by 4 by utilising the OX16C95x Times clock register (TCR). The driver can
multiply this baud rate, or divide it using the Clock Prescaler register (CPR).
The clock pre-divisor is used to divide the input clock prior to baud rate generation. This means a high
speed crystal (e.g. 50MHz) can be pre-divided to generate standard baud rates (In this case 50 / 27.125 =
1.8433 MHz, which will emulate a 1.8432 MHz crystal with less than 0.01% bit rate error). Alternatively, the
pre-divisor could be switched off to allow data rates up to 12.5Mbps to be generated.