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AR# 8985

Virtex Configuration - Virtex, Virtex-E, Virtex-II, Spartan-II/-E device limit in serial daisy chain configuration


General Description:

There is a hard limit to the amount of data that can be passed to the DOUT pin in a daisy chain (either Master or Slave Serial) for Virtex/-E, Virtex-II, and Spartan-II/-E devices.


Virtex/E, Spartan-II/E

The maximum amount of data that can be sent to the DOUT pin for a serial daisy chain for Virtex/-E and Spartan-II/-E devices is 2^20-1 (1,048,575) 32-bit words, or 33,554,400 bits. The configuration bitstream of downstream devices is limited to this size.

Virtex-II/II Pro, Spartan-3

Virtex-II/II Pro and Spartan-3 devices are limited to 2^27 -1 (134,217,727) 32-bit words, or 4,294,967,264 bits.


1. This applies to serial daisy chains only (configurations that use the DOUT pin to pass data on). This Answer Record does not apply to JTAG, as there is no limit to the size of a JTAG chain.

2. For more information on how an FPGA passes data to its DOUT pin, please see to (Xilinx Answer 7891).

For example:

A V1000 requires just over 6,000,000 configuration bits. This means that no more than six V1000 devices can be connected in a (master/slave) serial chain (since the first device will have to shift out 5 * 6,000,000 = 30,000,000 bits)

AR# 8985
Date Created 08/21/2007
Last Updated 12/15/2012
Status Active
Type General Article