20 www.xilinx.com Virtex-4 FPGA Configuration User GuideUG071 (v1.12) June 2, 2017Chapter 1: Configuration Overview RLoad Configuration Data Frames (Step 6)After the synchronization word is loaded and the device ID has been checked, theconfiguration data frames are loaded. This process is transparent to most users. For details,refer to Chapter 7Cyclic Redundancy Check (Step 7)As the configuration data frames are loaded, the device calculates a Cyclic RedundancyCheck (CRC) value from the configuration data packets. After the configuration dataframes are loaded, the configuration bitstream can issue a Check CRC instruction to thedevice, followed by an expected CRC value. If the CRC value calculated by the device doesnot match the expected CRC value in the bitstream, the device pulls INIT_B Low andaborts configuration. The CRC check is included in the configuration bitstream by default,although the designer can disable it if desired. (Refer to the Development System ReferenceGuide, BitGen section.) If the CRC check is disabled, there is a risk of loading incorrectXC4VLX200 01734093Notes:1. Does not reflect the actual device array size.Table 1-7: Signals Relating to the Device ID CheckSignal Name Type Access(1) DescriptionID_Err Status Internal signal. Accessedonly through the Virtex-4status register.Indicates a mismatch between thedevice ID specified in the bitstreamand the actual device ID.Notes:1. Information on the Virtex-4 status register is available in Table 7-9. Information on accessing the JTAGcapture sequence is available in Table 8-4.Table 1-6: Virtex-4 Device ID Codes (Continued)Device IDCODE Device IDCODE Device IDCODEFigure 1-8: Load Configuration Data Frames (Step 6)DevicePower-UpSample ModePins Synchronization Device IDCheck CRC CheckClearConfigurationMemoryStartupSequenceLoadConfigurationDataStart Finishug071_08_122105BitstreamLoadingSteps1 2 3 4 5 6 7 8Figure 1-9: Cyclic Redundancy Check (Step 7)DevicePower-UpSample ModePins Synchronization Device IDCheck CRC CheckClearConfigurationMemoryStartupSequenceLoadConfigurationDataStart Finishug071_09_122105BitstreamLoadingSteps1 2 3 4 5 6 7 8
