Cyclone II devices support IOE I/O standard reconfiguration through the JTAG BST chain. The JTAG chain can update the I/O standard for all input and output pins any time before or during user mode through the CONFIG_IO instruction. You can use this capability for JTAG testing before configuration when some of the Cyclone II pins drive or receive from other devices on the board using voltage-referenced standards. Since the Cyclone II device might not be configured before JTAG testing, the I/O pins may not be configured for appropriate electrical standards for chip-to-chip communication. Programming the I/O standards via JTAG allows you to fully test I/O connections to other devices.