31.10.3 PROG_ENABLE (0x4)

The AVR specific public JTAG instruction for enabling programming via the JTAG port. The 16-bit Programming Enable Register is selected as data register. The active states are the following:

• Shift-DR: the programming enable signature is shifted into the data register.
• Update-DR: the programming enable signature is compared to the correct value, and Programming mode is entered if the signature is valid.