S1 enables / disables the communication between the Cypress EZ-USB FX2 microcontroller and the I2C CMOS Serial EEPROM.
Turn S1 off when programming the USB EEPROM (storing the USB vendor ID and device ID). This will force the USB microcontroller to provide its default vendor ID and device ID.

S1

position

ON (lightbulb)*

EEPROM enabled

OFF (grey lightbulb)

EEPROM disabled

For further information, please read this  Configuration paragraph.