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 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: