Focussz Fosc21

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Focussz Fosc21

The Focussz Fosc21 is a USB-based, 2-channel oscilloscope with an analog bandwidth of 3kHz and a sampling rate of 8kHz (1 channel) / 4kHz (2 channels). The manufacturer improperly calls this device an oscilloscope: It can only measure voltages from 0-5V, and thus cannot measure negative voltages.

See Focussz Fosc21/Info for more details (such as lsusb -v output) about the device.


  • Main chip: ST STM8S103 (marking: "STM8S103-K3T6C 990XB F6 MYS 136")
  • USB interface: Prolific PL-2303HX (marking: "PL-2303HX LE10193A")
  • Crystals: 12.000 and 22.1184



The USB connector is a PL2303 USB serial adapter. The port settings are 115200, 8n1.

The protocol is currently being analyzed. This section will be updated with details at a later time.

For more details see User_talk:Mrnuke#Focussz_Fosc21_Protocol.