The FT232RL stores its USB manufacturer, product, and serial-number descriptors in its internal EEPROM. The browser tool above rewrites those strings through WebUSB, recalculates the FTDI checksum, and leaves unrelated configuration words intact.
Before Writing the EEPROM
Close serial terminals and any application using the adapter before connecting. The operating system normally claims FTDI devices, so browser access may depend on platform permissions and driver state. Empty manufacturer and serial fields preserve their existing values; the product field is always replaced.
An interrupted or incorrect EEPROM write can change enumeration behavior. Keep the adapter directly connected, avoid hubs with unstable power, and do not unplug it while the tool reports that it is writing. After a successful update, physically unplug and reconnect the device because USB descriptors are read during enumeration.
What Else Is Stored in the FT232R EEPROM?
The EEPROM also contains the USB vendor and product IDs, power attributes, remote-wakeup settings, inversion options, CBUS pin functions, drive-current choices, and device-family configuration. Those fields affect driver matching and electrical behavior. This tool deliberately does not expose them: changing a VID/PID can prevent the expected driver or WebUSB filter from finding the adapter, while an unsuitable CBUS or power configuration can alter connected hardware.
WebIO reads all 64 EEPROM words, rebuilds only the descriptor region beginning at byte 0x18, recomputes the checksum stored in word 0x3F, and writes the image with programming latency. FTDI's FT_PROG utility remains the appropriate choice for complete device templates, read-back verification, and recovery workflows.
References
- [FTDI2020]Future Technology Devices International, FT232R USB UART IC Datasheet.
- [FTDI2023]Future Technology Devices International, AN_124: User Guide for FT_PROG.
- [WebUSB]W3C Web Platform Incubator Community Group, WebUSB API.