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AR# 2017

FPGA Configuration: Difference between the preamble/length count of XC4000/E/EX and the XC5200

Description

What is the difference between the XC4000/E/EX length count

and the XC5200 length count?

Solution

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.

AR# 2017
Date Created 08/21/2007
Last Updated 05/07/2014
Status Archive
Type General Article