Document No.: FT_000053
FT232R USB UART IC Datasheet Version 2.07
Clearance No.: FTDI# 38
7.6 Using the External Oscillator
The FT232R defaults to operating using its own internal oscillator. This requires that the device is
powered with VCC(min)=+4.0V. This supply voltage can be taken from the USB VBUS. Applications which
require using an external oscillator, VCC= +3.3V, must do so in the following order:
1. When device powered for the very first time, it must have VCC > +4.0V. This supply is available
from the USB VBUS supply = +5.0V.
2. The EEPROM must then be programmed to enable external oscillator. This EEPROM modification
cannot be done using the FTDI programming utility, MPROG. The EEPROM can only be re-
configured from a custom application. Please refer to the following applications note on how to do
this:
http://www.ftdichip.com/Documents/AppNotes/AN_100_Using_The_FT232_245R_With_External_
Osc(FT_000067).pdf
3. The FT232R can then be powered from VCC=+3.3V and an external oscillator. This can be done
using a link to switch the VCC supply.
The FT232R will fail to operate when the internal oscillator has been disabled, but no external oscillator
has been connected.
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