Virtex®-4 FPGAs use CMOS Configuration Latches (CCLs) to enable configurable interconnects between routing lines and logic cells. Virtex-4 FPGAs are volatile devices - they do not retain their configuration when power is removed. To configure a Virtex-4 FPGA, you must reinitialize the CCLs inside the device each time power is cycled. Power up configuration for Virtex-4 FPGAs varies by application.
Customers who are in the prototyping phase have the following options for Virtex-4 FPGA configuration:
In the field, customers must implement a non-volatile configuration memory solution to configure Virtex-4 FPGAs. Xilinx offers the following options:
Simplest configuration scheme, serial throughput.
The Xilinx FPGA drives the Xilinx PROM CLK as the Xilinx PROM provides serial (x1) configuration data to the Xilinx FPGA.

The Xilinx PROM’s internal oscillator drives the Xilinx FPGA CCLK as the Xilinx PROM provides serial (x1) configuration data to the Xilinx FPGA.

An external clock drives the Xilinx PROM CLK and the Xilinx PROM drives the Xilinx FPGA CCLK as the Xilinx PROM provides serial (x1) configuration data to the Xilinx FPGA.

An external clock drives both the Xilinx FPGA CLK and the Xilinx PROM CLK as the Xilinx PROM provides serial (x1) configuration data to the Xilinx FPGA.

Parallel configuration for fastest throughput.
The Xilinx FPGA drives the Xilinx PROM CLK as the Xilinx PROM provides byte-wide (x8) configuration data to the Xilinx FPGA.

The Xilinx PROM’s internal oscillator drives the Xilinx FPGA CCLK as the Xilinx PROM provides byte-wide (x8) configuration data to the Xilinx FPGA.

An external clock drives the Xilinx PROM CLK and the Xilinx PROM drives the Xilinx FPGA CCLK as the Xilinx PROM provides byte-wide (x8) configuration data to the Xilinx FPGA.

An external clock drives both the Xilinx FPGA CCLK and the Xilinx PROM CLK as the Xilinx PROM provides byte-wide (x8) configuration data to the Xilinx FPGA.
