The aWire interface makes use the /RESET wire of the Atmel AVR device to allow programming and debugging functions. A special enable sequence is transmitted by the Atmel AVR ONE!, which disables the default /RESET functionality of the pin.

When designing an application PCB, which includes an AVR with the aWire interface, it is recommended to use the pinout as shown in Figure 1. The AVR ONE! ships with both 100-mil and 50-mil adapters supporting this pinout.

Figure 1. aWire Header Pinout

Tip: Since aWire is a half-duplex interface, a pull-up resistor on the /RESET line in the order of 47k is recommended to avoid false start-bit detection when changing direction.

The aWire interface can be used as both a programming and debugging interface, all features of the OCD system available through the 10-pin JTAG interface can also be accessed using aWire.