I/O Through Printer Port

[<ABX]

activate code when circut is brokin. Like alarm system?

[Jim Brown]

I think you would need to have some code running all the time, examining the port every now-and-then with a timer. Have the electronics of the alarm put say a 1 on one of the pins that the port uses for status, like the PaperOut pin, for normal circumstances. Then if the alarm is triggered have that change to 0 and then when your code sees a 0 on the pin it branches to another part of the program.

Two useful sites for this sort of thing are Boondog and Lakeview Research:

http://www.boondog.com
http://www.lvr.com

and attached is a short note I wrote about examining and setting pins.