I have a design targeting a pre 7 series device (e.g., Spartan-6) in the ISE design tools.
When I try to import the ISE design into Vivado, I find that a Virtex-7 (7v485T) device is selected instead of the original Spartan-6 device.
What is the possible reason for this device change after importing?
The Vivado tool has been created for the high performing 7 series devices (Virtex-7, Kintex-7, Artix-7, and Zynq-7000). As new device families are developed and released by Xilinx, they will also be supported with the Vivado tool set. However, there is no plan to support earlier device families in the Vivado tool. For these families, please use the ISE Design Suite.
Example: When you attempt to import your Spartan-6 ISE design to Vivado, due to the non-availability of the Spartan-6 device in the Vivado device list, the tool selects a default device (7v485T).
Observe that in the "Select Device" option of the Vivado tool, there are no Spartan-6 devices listed for selection (as shown in the following image). The devices that are supported in the Vivado tool are Virtex-7, Kintex-7, Artix-7, and Zync-7000.
To support the Spartan-6 devices (or any non-7 series devices), you need to use the latest ISEdesign tools which works best regardless of the complexity of the design.