Clock Mode _xinfreq "plus some error"?

RonP

Hello All,

I'm working my way through the HYDRA book. I've had a lot of "AHA" moments. Can't say I understand everything, but my Prop Education is looking good.

I've got this one question in the code below " + 0000 " does what? I haven't seen " + 0000 " before except in a few Objects from the exchange. And can't find it explained in any documentation that I have. PEK, Prop Manual, Data Sheet.

CON

  _clkmode = xtal2 + pll8x              ' enable external clock and pll times 8
  _xinfreq = 10_000_000 + 0000          ' set frequency to 10 MHZ plus some error
  _stack = ($3000 + $3000 + 64) >> 2   ' accomodate display memory and stack

Any explanation would be great, or a pointer on where to look. :cool:

Thanks
-Ron

Phil Pilgrim (PhiPi)

For video stuff in particular, it's helpful to be able to fudge the crystal frequency value a little, since no crystal is perfectly on frequency. Crystals that are a hair off-frequency typically manifest the error as faint vertical or diagonal color bars on the screen or with a phenomenon variously called "zipper" or the "creepy crawlies" noticeable on the edges of high-contrast vertical image features.

-Phil

RonP

Thanks Phil

It keeps the "creepy crawlies" away, I should have known.
Well it makes perfect sense now. I can continue with the HYDRA book now and not wonder what + 0000 is for.

-Ron