FT232R datasheet(29/40 Pages) FTDI

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FT232R USB UART IC Datasheet

Version 2.16

Document No.: FT_000053 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, FT_PROG. The EEPROM can only be re-

configured from a custom application. Please refer to the following applications note on how to do

this:

AN_100_Using_The_FT232_245R_With_External_Osc

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.

FT232R Datasheet(PDF) 29 Page - Future Technology Devices International Ltd.