The asynchronous serial port can transfer up to 300 kbytes/s of data assuming
one Start bit and one Stop bit per byte.
Five additional pins form the configurable CBUS. The pins are programmable
via a utility provided by FTDI and can have these functions:
??? LED driver that pulses when transmitting or receiving via USB.
??? Output that goes low when the device is in the USB Suspend state.
??? General-purpose I/O.
??? Output that goes high when data is transmitting on TXD. The output can
interface directly to the transmit-enable input of an RS-485 transceiver,
eliminating the need to enable the transmitter using firmware or additional
hardware.
??? Configurable clock output for driving an external CPU or microcontroller.
Using Special-function USB Controllers
327
The chip can obtain its power from the VBUS line in the USB cable or from an
external supply that connects to the VCC pin. The 3V3OUT pin is a +3.3V
output. VCCIO is an input whose voltage determines the logic levels on the
UART and CBUS pins. The pin can connect to VCC, 3V3OUT, or an external
supply. The chip doesn??™t require an external oscillator.
To convert the asynchronous serial interface to RS-232, use a Maxim MAX232
or similar interface chip. To convert to RS-485, use an SN75176B or similar
RS-485 transceiver.
Figure 15-1: The FT232R converts between USB and asynchronous serial data.
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