plotting the step function through Maxima

Dear Maxima' s users,

I need to draw the step function through Maxima. I used this syntax to draw
the graph of a step function.

y:1-2*unit_step(t-1)+unit_step(t-2);

wxplot2d(y,[t,0,3]);



 However, it is mathematically wrong. Because it does not meet requirements
of the function. Could you please guide me to use the appropriate syntax?

Thank you,

Fereshteh