TV_Text Demo with external resonator
tatatom
Posts: 16
Hi
Firstly greetings to all. I just signed up after getting my Prop working on a home-made board. Looks like lots of fun learning ahead.
So my board has a 20 mhz external resonator hooked up and does work with the simple blink LED program. So feeling supremely confident I jumped right to the TV_Demo program , wired up the video out and ... nothing. I think I need to change the
_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000
at the top of the program to accommodate the 20 mhx resonator. If this is true how do I determine the correct value? I tried various settings but nothing made any difference. If I need to do something else , then I'd appreciate a nudge in the correct direction.
Thanks
Tom
Firstly greetings to all. I just signed up after getting my Prop working on a home-made board. Looks like lots of fun learning ahead.
So my board has a 20 mhz external resonator hooked up and does work with the simple blink LED program. So feeling supremely confident I jumped right to the TV_Demo program , wired up the video out and ... nothing. I think I need to change the
_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000
at the top of the program to accommodate the 20 mhx resonator. If this is true how do I determine the correct value? I tried various settings but nothing made any difference. If I need to do something else , then I'd appreciate a nudge in the correct direction.
Thanks
Tom
Comments
You have to use just XTAL2. This is for an external crystal/resonator in the range 8 - 32MHz without using the PLL (which won't work at 20MHz). _xinfreq is 20_000_000. The minimum system clock for NTSC TV is about 15MHz so you're ok there.
Still having problems though. The TV display is totally garbled and no amount of adjusting the TV will stabilize it. have tried several different TVs with the same results. I put in a new resonator and no difference either. Also tried a different Prop chip.
All connections checked with Digital meter.
The resistance at P12 is 1.095K as oppose to the 1.1K called for
The resistance at P13 is 557 as oppose to the 560 called for
The resistance at P12 is 276 as oppose to the 270 called for
Do I need trim pots or something? Is there some adjustment somewhere that I could do and as a last resort is it possible to do this without an external resonator?
The first lines of the TV_Text_Demo have been changed to:
CON
_clkmode = xtal2
_xinfreq = 20_000_000
thanks again
Tom
I'm going to order some today and move on to discovering more about the prop chip in the meantime.
Thanks for the help.
Tom
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Stan Dobrowski
Mike, I am·missing something...
1) Can you not use 20Mhz·XTAL2 + PLL4X per table 4-4 'Valid clock Mode Expressions'· for 80MHz operation? I also don't see anything in the TV object preventing·the use of this mode... Post Edit: Oops, just found the PLL·XIN range of 4-8Mhz (Table 1-7 PLLENA)
2) Could this problem be that the 20MHz resonator is not actually close enough to 20MHz and feeding·the·actual frequency into the code may stabilize the display?
Post Edited (Don D) : 3/7/2007 9:29:57 PM GMT
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
The comments in the source for TV.spin say that the minimum clock is 4 x color burst frequency = about 15MHz for NTSC, 18MHz for PAL.
If you have an oscilloscope or frequency counter, you can write some code using the couter to output the frequency the propeller is operating at and meaure it's actual value.
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
Post Edited (Paul Baker (Parallax)) : 3/7/2007 10:25:56 PM GMT
_clkmode = xtal1 + pll16x
_xinfreq = 4_000_000
and it worked perfectly.
I will leave it to those who know more than I do to draw whatever conclusions.
I'm just happy to see it work this way until my 5mhz crystals arrive.
Tom
Pat