Are you using WDT ? You could lose the CLRWDTs otherwise

>      __CONFIG  & _WDT_ON &

My quick back-of-envelope calcs suggest the DELAY500
routine is taking almost 8,000,000 cycles. To be done in 500ms
that would imply a 64MHz crystal  (64,000,000/4/2)

(Ignoring 2-cycle DECFSZ)

(4 x 9) x (4 x 169) x (4 x 81) = 7,884,864

At 4Mhz (1us instruction time) this would take 8 seconds

Assuming I'm right (lot on today, I feel like an octopus
playing the drums), and your 500ms isn't critical, use
a WDT interrupt for timing (would take about 28 at 18ms
each), or just a two-level nest. Get the internal loop to
around 2000 cycles with NOPs and a 0-255 count for the
external, if you're running at 4MHz. If you want exactly
500ms you'll have to get the calculator out and take a
look at the timing routine suggestions at www.piclist.com

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