Can a plugin tell which key invoked it? (for uppercasing)

I need to convert lowercase letters to uppercase as the user types. (This is only for certain types of paragraph, which I determine by looking at the CSS class name of the p tag.) I began writing a plugin to do this, but I found that when I map a plugin to a letter key the letter doesn't get inserted into the text. I could add the letter if I knew what it was. I could of course write 26 plugins, 1 each for "a" through "z", but I would like to avoid that if there's a better way.

So my questions are:
1. is there a way to have the key that invoked the plugin still be processed before the plugin runs?
2. if not, is there a way to determine which key invoked the plugin?

Thanks,
Steve