Various techniques are provided for determining interface characteristics of external devices. In one example, a method of configuring a programmable logic device (PLD) with configuration data stored in one or more external memory devices includes reading by the PLD an interface setup command in a bitstream from an external memory device through a configuration port of the PLD while operating the configuration port in accordance with a first set of interface characteristics. The method also includes adjusting by the PLD the configuration port to operate in accordance with a second set of interface characteristics identified by the interface setup command. The method also includes reading by the PLD configuration data in the bitstream from the external memory device through the configuration port while operating the configuration port in accordance with the second set of interface characteristics. The method also includes programming a configuration memory of the PLD with the configuration data.