Teardown: Nokia USB interface (USB to UART)

This is clone of Nokia DKU-5 USB cable sold under the "Blue Star" brand. Bought to be used as a USB to UART converter. As many other mass products - extremely cheap.
Easy to open: two parts of case were not clued together, turn slightly plastic part that holds cable to help opening.

Inside: OTI6858 USB to UART converter:
  • '51 MCU core
  • USB 1.1 Full-Speed
  • up to 3 Mbps

It has 3.3V output levels. Missing parts (L3, U3, K1) suggest some kind of optional DC-DC converter with output connected to K1.
U2 = external EEPROM for PID, VID, serial number, USB max power descriptor, LED configuration, etc.

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