The aWire interface makes use of the RESET wire of the AVR device to allow programming and debugging functions. A special enable sequence is transmitted by the Atmel-ICE, which disables the default RESET functionality of the pin.
When designing an application PCB, which includes an Atmel AVR with the aWire interface, it is recommended to use the pinout as shown in Figure 1. Both 100-mil and 50-mil variants of this pinout are supported, depending on the cabling and adapters included with the particular kit.
Since aWire is a half-duplex interface, a pull-up resistor on the RESET line in the order of 47kΩ 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.