I have an Avocent SwitchViewDVI (4SVDVI10) KVM that looks to be run by an ATmega64 microcontroller. Every now and then the KVM locks up and I need to reset the unit by pulling all USB power sources to it, a considerable hassle to access.
I know that the ATmega64's pin 20 is a reset and according to the datasheet "a low level on this pin for longer than the minimum pulse length will generate a reset". I suspect this can be used to provide a more convenient reset than pulling all power. I know a bit about electronics and am good with an iron, but microcontrollers are new territory for me. I'm a geek, but without proper EE cred.
There is a 21k Ohm resistor between VCC and the reset pin, I assume "pulling reset high" is possibly for power-on reset. My theory is that if I "pull low" (ground) the reset pin (easiest attach point being the reset side of the resistor) via a momentary switch I can generate that reset signal.
- Is this correct?
- Do I need to open the circuit between reset and VCC?
- Should I include a resistor between the reset pin and ground to be a current limiter?
My suspicion is I need to keep VCC attached via the 21k Ohm resistor and use a resistor between reset and ground to form a divider, as the datasheet specifies a reset pin threshold voltage range of 0.2VCC-0.85VCC. Since VCC via USB should be somewhere around the 5V USB spec (I measured 4.1V in testing) I'm thinking a 3k Ohm resistor between reset and ground should get me there.
I'm sure this is very EE 101 and I welcome responses/critiques of my described problem.