The USB ports on the back of the radio are used to control external RS232 devices and non RS232 devices.
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This genuine FTDI interface cable plugs into the USB port on the back of the FLEX-6000 series radios to connect to devices requiring a parallel
USB to Parallel adapter for the FLEX-6000 series
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Flex 6000 - What is the USB port for on the back of the radio : FlexRadioSystems : Free Download, Borrow, and Streaming : Internet Archive