4.3.4 aWire Physical Interface

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 Power Debugger, 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 4-8. Both 100-mil and 50-mil variants of this pinout are supported, depending on the cabling and adapters included with the particular kit.

Figure 4-8. aWire Header Pinout
Tip:

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.