Copyright © 2010 Future Technology Devices International Limited

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Document No.: FT_000052

FT245R USB FIFO IC Datasheet Version 2.10

Clearance No.: FTDI# 39

8.2 Using the External Oscillator

The FT245R 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

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 FT245R 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 FT245R will fail to operate when the internal oscillator has been disabled, but no external oscillator

has been connected.