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 a Microchip 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 47 kΩ 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.