Functional Description

USB2SER Data Sheet, Rev. 0

Freescale Semiconductor

9

Figure 7. Example schematic using an RS232 transceiver

2.4

UART Baud rates

Baud rate is calculated by generating an internal divisor used to generate the clock for the UART communication module. The

following calculation is used to estimate the real baud rate that will be generated by the device:

Where

is the closest integer resulting from the division.

After reset the device is automatically configured to communicate at 115,200 bps which is the maximum allowed value.

2.5

Flow control operation

The device works as a standard Communication Device Class (CDC); to add flow control options to this class, the drivers are

installed in the operating system to enable this functionality.

When working without any flow control option, it is possible to generate an overflow condition, if the USB host does not request

for the data received through the serial interface fast enough. Using any flow control option (hardware or software) eliminates

the overflow possibility.

The following formula may be used to determine the amount of time without requesting data to generate the overflow condition:

BaudRate

24 000 000



Round

24 000 000



DesiredBaudrate

16



---------------------------------------------------------





16



---------------------------------------------------------------------------------------------

=

Round

24 000 000



24 000 000



DesiredBaudrate

16



---------------------------------------------------------





---------------------------------------------------------------

=