tv_driver xtal problem

booker88

i am new to the propellor and this might be a stupid question, but
i have a propellor on a breadboard and i'm trying to do spin lesson 9 (using tv_terminal).

i'm having problems with the tv syncing to the ntsc signal. i don't have a 5 mhz xtal, but i tried to use a 20 mhz crystal as follows

_clkmode = xtal2 + pll4x
_xinfreq = 20_000_000

then i tried a using a 4.194304 mhz crystal using

_clkmode = xtal1 + pll16x
_xinfreq = 4_194_304

it works with this crystal, but the text is flickery, i thought that as long as the freq was high enough it wouldn't matter.
can anyone tell me what i'm doing wrong?

Phil Pilgrim (PhiPi)

The PLL is only guranteed to function with crystals between 4MHz and 8MHz, although it appears to work with somewhat higher frequencies. 20MHz, however, is way out of range. There is more to a crystal than frequency, though. There are also resonance mode (serial or parallel) and capacitance. The Propeller needs to have a parallel-resonant crystal of around 20pF (5MHz). A series-resonant crystal, or one with a different capacitance, may not oscillate at the specified frequency, which is why you're not getting the video to sync. Even a slightly bad connection may lead to the frequency being off, as I discovered when I repaired a suspicious crystal solder joint on a board that wouldn't produce color video.

Just as a test, I rummaged through my junk box and found two crystals marked "4.9152MHz". One produced stable video, but no color, indicating a slightly off frequency. The other produced stable video and color, but there was fringing that may betray either a slightly off frequency or excessive PLL jitter.

My recommendation would just be to purchase the correct 5MHz crystal and be done with it.

-Phil