(My knowledge of analog circuit design is severely limited).
I am trying to generate a reset pulse for an AVR microcontroller. The reset is active LOW, and the maximum threshold voltage is 0.9V, with a pulse of no less than 2.5us.
I am trying to generate the required pulse from the DTS line of an RS232-Level signal. This means that the DTS line voltage is from ~-13V (inactive) to ~+13V (active).
This is the best I could come up with, and it does not work. I have simulated using Spice, and depending on the ramp of the positive edge of the DTR pin, the RESET_N may never go under 2.5v.
The simulation from CircuitLab:
The simulation from NI Multisim:
EDIT: Added Voltage points to the AVR Circuit to clarify that GND is common.