 There is no area for any additional circuitry, although this can be provided by a third-party product called the "Dragon Rider".The JTAG In Circuit Emulator (JTAGICE) debugging tool supports on-chip debugging (OCD) of AVRs with a JTAG interface.The original JTAGICE (sometimes retroactively referred to as JTAGICE mkI) uses an RS-232 interface to a PC and can only program AVR's with a JTAG interface.