Oops! I searched for "PWM" in the 'C84 Data Sheet, on CD-ROM, to see if it had a PWM before I sent my reply. I didn't want to look foolish ya know. I found a reference and off went my note. Oh well. If I had actually read what it said I would have realized it said that the 'C84 doesn't have a PWM. I am using a 'C73 with all those gizmo's. Sorry How about a Brute force software PWM. Are any of your timing loops less than the period of the highest frequency you want to use in your siren? Mark "How about the "Popeye" theme at 130dB?" Jurras >>> Gregg Kricorissian 9 October 1996 7:51 pm >>> At 01:23 PM 10/9/96 -0400, Mark Jurras wrote: >How about the PWM on board the 'C84 otherwise a NE555 with a few RC networks >and a couple control lines from the PIC could do it. >>>> Gregg Kricorissian Request: >I'm using a 16C84 for an alarm controller, and I'd like to use the PIC to >also generate a "siren" waveform (to be externally amplifed), rather than >build that function in separate hardware. etc etc... Hi Mark, Many thanks for the quick response. However, unless I'm mistaken, the 'C84 is not the one with the internal PWM. Control lines from the PIC in this design are now fully allocated, and all I have to left for the alarm function is a simple enable. I've thought about using a CMOS 555 to generate the waveform, but the siren IC's do the whole banana in the same real estate as one 555 ... also, no external components required. Kind of hard to beat .... Let's see what the list can turn up. Cheers, ....Gregg