Interrupt Service Routine (continued)

• //------------------------------------------------
• // keep the max & min samples during 2nd cycle
• //------------------------------------------------
• if (tick20Count >= 20)
• {
• if (Output > max_sample)
• max_sample = Output;
• if (Output < min_sample)
• min_sample = Output;
• }
• //------------------------------------------------
• // increment a count of 40 samples across
• // a pair of 60hz cycles (20 counts per cycle)
• // 20*1/1200 sec = 1/60 sec
• //------------------------------------------------
• tick20Count++;
• //------------------------------------------------
• // toggle a digital output each 60hz cycle
• //------------------------------------------------
• if (tick20Count == 20) LATB0 ^= 1;

• tick20Count is counting interrupts of each input. If we’re observing the 2nd 60 Hz cycle, observe (and save) max and min values of Output.
• Then, perform the actual increment of “tick20Count”

• LATB0 is toggled merely to observe the 60Hz interrupt service cycles on an unused PIC output for diagnostic purposes.