Very nicely done :) I never got around to integrating the protocol with a debugger. It seems like your usb-serial adapter got a pullup builtin because without a 10k pullup on reset debugwire does not work. I used a npn or pnp transistor on the tx pin to convert to open collector but a low Vf diode is even simpler if one is available. (Using npn: TX - Emitter, Vcc - 10k - Base, Vcc - 10k - Collector - Output) (Using pnp: TX - 470R - Base, Collector - Ground, Vcc - 10k - Emitter - Output)
Very nicely done :) I never got around to integrating the protocol with a debugger. It seems like your usb-serial adapter got a pullup builtin because without a 10k pullup on reset debugwire does not work. I used a npn or pnp transistor on the tx pin to convert to open collector but a low Vf diode is even simpler if one is available. (Using npn: TX - Emitter, Vcc - 10k - Base, Vcc - 10k - Collector - Output) (Using pnp: TX - 470R - Base, Collector - Ground, Vcc - 10k - Emitter - Output)