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AR# 10850

1.0 J Drive - How do I determine the length of a device's instruction register (IR)?


General Description:

When using JTAG Programmer or JDRIVE, it is sometimes necessary to know the length of a device's Instruction Register. How do I determine the length of the IR?


The easiest way to find the length of a device's Instruction Register is to look in the BSDL file for that device. The IR length is defined in the following line:

attribute INSTRUCTION_LENGTH of [Device] : entity is [length];

For example:

For an XCV100 BG256, this line would read:

attribute INSTRUCTION_LENGTH of XCV100_BG256 : entity is 5;

Some IR lengths for commonly used Xilinx device families:

Virtex/E: IR=5

18Vxx: IR=8


AR# 10850
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article