I'd like a way to make LTSpice report an error if one of my sub-circuits detects an invalid condition. For example, I often simulate a PIC by representing it as a sub-circuit that applies signals to its pins in accordance with the way I intend to program it. I'd like that sub-circuit to check, for example, that it has the correct voltage on its power and ground pins, and flag an error if not.
Anyone have a way of doing that?
Sylvia.
LTspice will report the results of measurements which can contain calculations. If you have a value called "VoltageTooLow" and calculate it by dividing by a value which would be exactly zero when your error condition occurs, rather than reporting a number it will flag the error... I think. I know I had what look like error reports when my measure statements were not able to be executed.
Otherwise you can create a signal that makes an extreme change in voltage when the error condition occurs and monitor it on the waveform display. Switches are useful for bounds checking.
I had thought of division by zero. It doesn't work. Nor does sqrt(-1). Having a signal whose voltage indicates an error is less effective because it requires one to remember to check it.
Sylvia.
I can get it to report that Vcc is not above a threshold.
.MEAS TRAN VccCheck FIND V(Vdd) WHEN V(Vdd)>3.45
Measurement "vcccheck" FAIL'ed
This is a bit backwards, but this will report the voltage if it is above the threshold at any time or give the error if it never goes above.
Depending on the nature of your power rail you could check directly for a voltage below the threshold. If it finds it it will report the voltage. If it is *never* below the threshold it will give the error message. If the voltage ramps up or is within spec at any time this will not find the improper voltage.
Check out Bounding_Circuits.zip on the Device Models & Subcircuits Page of my website.
That may be of help. ...Jim Thompson
Have something to add? Share your thoughts — no account required.
Ask the community — no account required