Enable DTR/RESET by software with an ATMega328 MCU
Do you mean something like this?

When "CONTROL" is driven HIGH:

DTR is HIGH, the N-FET is OFF (Vgs = 0), and RST is HIGH.

DTR is LOW, the N-FET is ON (Vgs = 5V)and pulling RST LOW.

When "CONTROL" is driven LOW:

DTR is HIGH, the N-FET is OFF (Vgs = -5V), RST is HIGH.

DRT is LOW, the N-FET is OFF (Vgs = 0V), RST is HIGH.

When "CONTROL" is in high impedance state:

R3 pulls N-FETs gate up, connecting DTR and RST when DTR goes LOW. 

So basically, when CONTROL is HIGH, DTR is enabled.







simulate this circuit &ndash; Schematic created using CircuitLab