3.6 Connecting to a debugWIRE Target

The recommended pinout for the 6-pin debugWIRE (SPI) connector is shown in Table 3-6.

Connection to a 6-pin 100-mil SPI Header

Use the 6-pin 100-mil tap on the flat cable (included in some kits) to connect to a standard 100-mil SPI header.

Connection to a 6-pin 50-mil SPI Header

Use the adapter board (included in some kits) to connect to a standard 50-mil SPI header.

Connection to a custom 100-mil Header

The 10-pin mini-squid cable should be used to connect between the Atmel-ICE AVR connector port and the target board. Three connections are required, as described in Table 3-5.

Although the debugWIRE interface only requires one signal line (RESET), V_CC, and GND to operate correctly, it is advised to have access to the full SPI connector so that the debugWIRE interface can be enabled and disabled using SPI programming.

When the DWEN fuse is enabled, the SPI interface is overridden internally for the OCD module to have control of the RESET pin. The debugWIRE OCD is capable of disabling itself temporarily, thus releasing control of the RESET line. The SPI interface is then available again (only if the SPIEN fuse is programmed), allowing the DWEN fuse to be un-programmed using the SPI interface. If power is toggled before the DWEN fuse is un-programmed, the debugWIRE module will again take control of the RESET pin. Normally MPLAB X IDE or Atmel Studio will automatically handle the interface switching, but it can also be done manually using the button on the debugging tab in the properties dialog in Atmel Studio.

It is not possible to use the debugWIRE interface if the lockbits on the target AVR device are programmed. Always be sure that the lockbits are cleared before programming the DWEN fuse and never set the lockbits while the DWEN fuse is programmed. If both the debugWIRE Enable (DWEN) fuse and lockbits are set, one can use High Voltage Programming to do a chip erase, and thus clear the lockbits. When the lockbits are cleared, the debugWIRE interface will be re-enabled. The SPI Interface is only capable of reading fuses, reading signature, and performing a chip erase when the DWEN fuse is un-programmed.