Answers Database FPGA Configuration: Difference between the preamble/length count of XC4000/E/EX and the XC5200 Record #2017 Product Family: Hardware Product Line: 5200 Product Part: 5200 Problem Title: FPGA Configuration: Difference between the preamble/length count of XC4000/E/EX and the XC5200 Problem Description: What is the difference between the XC4000/E/EX length count and the XC5200 length count? Solution 1: The configuration data for XC4000/E/EX devices consist of a composite 40-bit preamble/length count. The configuration data for XC5200 devices consist of a composite 48-bit pream- ble/length count. Why is this the case? for 4k: ------- Fill Byte: 11111111b = FFh => 8 bits Preamble Code: 0010b = 2h => 4 bits Length Counter: COUNT(23:0) => 24 bits Fill Byte: 1111b = Fh =>+) 4 bits ---------- Total preamble/length count = 40 bits Therefore the .BIT file will have a preamble/length count of:                  FF20h and the PROM file will have a preamble/length count of:                  FF04h * Note: In the XC4000EX family of devices, this applies to        all configuration modes, except Express Mode. 4k        Express Mode does not have a length count. for 5k: ------- Fill Byte: 11111111b = FFh => 8 bits Preamble Code: 11110010b = F2h => 8 bits Length Counter: COUNT(23:0) => 24 bits Fill Byte: 11111111b = FFh =>+) 8 bits                           ----------         Total preamble/length count = 48 bits Therefore, the .BIT file will have a preamble/length count of:                   FFF2h and the PROM file will have a preamble/length count of:                   FF4Fh The additional 8 bits in the 5k preamble/length count comes from an additional 'F' prior to '4', and an additional 'F' after the length count. * Note: This also applies to 5k Express Mode, which does        have a length count. End of Record #2017 - Last Modified: 11/13/98 09:45

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