PIC16F628A blank composite video test

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Hi all a few month ago I stumbled across this site
http://www.rickard.gunee.com/projects and was compeled to get into
microcontrollers and do something similar. Anyway so I bough a
PIC16F628A and  JDM programmer. Now I am starting of simple so I made
this blank composite video test
http://home.aztec.aunz.com/dabski/VID_TEST.asm All it dose is create a
the syncs and leave the screen blank so that the TV can lock onto the
signal. Unfortunantly it dose not do this for some reason the TV dose
not detect the signal, when I run the program through a simulator with
an osciloscope eveything looks OK. Anyone go any ideas of what the
problem might be?


Re: PIC16F628A blank composite video test
Hi,

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 > Now I am starting of simple so I made this blank composite video test
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You are using the internal RC oscillator, which may not be accurate
enough for your TV set. Try a 4 MHz quartz, change oscillator config
accordingly. Have not looked through the code, though.

HTH
Wolfgang


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Re: PIC16F628A blank composite video test
Hmm I will have to try that will take me a while to get the 4MHz
crystal thought.


Re: PIC16F628A blank composite video test

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 > not detect the signal

BTW: How did you know your TV set did not detect the signal?
You are feeding it an all-black picture, don't you?

Wondering,
Wolfgang

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Re: PIC16F628A blank composite video test
I would know if the signal is being recieved because the screen stays
blue when no signal is detected. Also the simulator that I use dose not
show the oscilloscope properly you would only be able to see a small
part of the signal (around 30 frames). its not like a proper   CROW
that shows the whole signal. Apart from that their is no scale so you
can not tell for how the timming or anything from what it shows. All
you can see is weather the signal is high or low.


Re: PIC16F628A blank composite video test
Hi,


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Ah, OK, I see.

 > Also the simulator that I use dose not
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Well, in that case, it would be easiest to find somebody with
a suitable oscilloscope and check your output signal there.
I found that TV sets are quite tolerant on the scart/cinch inputs.

 > its not like a proper   CROW
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Which is of not much use here :-(
There must be a major problem in the signal generation.
Can you show the ciruit where you mix the BAS Signal together?

BTW: In your code you are using a 4MHz clock, which gives you
a 1 microsecond instruction time on PIC16. Then you select a
1:4 prescaler on timer 0, which gives you 4 microsecond steps
on timer 0. The comments in your source seems to assume
1 microsecond steps. So your signal is 4 times strechted,
no wonder your TV doen't recognize it.
I recommend using a 16MHz crystal on your PICs clock inputs.

regards,
Wolfgang

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Re: PIC16F628A blank composite video test
Here is the circuit http://home.aztec.aunz.com/dabski/circuit.PNG
Well around were I live I can only get 20MHz, 10MHz, 8MHz and 4 MHz.
For som reason I assumed that if I was running the PIC @ 4MHz that it
was executing 1 instruction per cycle thus 4 million instructions per
cycle so if I got a quater of that it would give me 1 instruction per
mS?

Anyway would I be correct to assume then from what you have said above
that if I turrned off the prescaler that the timmer would be then
giving me one beat per mS since I can not get hold of a 16MHz crystal?


Re: PIC16F628A blank composite video test
Damn I don't know how to edit my post so I am gona have to double post.
When I said mS i actually ment uS (microseconds).


Re: PIC16F628A blank composite video test
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Normally just move the cursor with rodent or arrows, then play with
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Please learn to include context.  Quick instructions below, more at
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Re: PIC16F628A blank composite video test

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A PIC running at 4MHz will execute 1 single-cycle instruction per
microsecond (uS).  The 4MHz clock (Fosc) is internally divided by 4 to
create the main clock signal.

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You really need to read the datasheet.  You should also find an LED
blinky program to verify that your PIC is indeed running.  BTW, most
people want PWRTE turned on.  TMR0 does not increment for 2 tick times
after modifying the value of it.

BTW, SUBLW subtracts W from the Literal, not the other way around.
http://www.brouhaha.com/~eric/pic/subtract.html


Re: PIC16F628A blank composite video test


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There should be also at least one resistor from /MCLR to Vcc?




Re: PIC16F628A blank composite video test
Nope I have disabled the MCLR so that it can be used as a normal I/O
pin.


Re: PIC16F628A blank composite video test

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Can you post some scope photos of the video
signal you're generating?

Don't post them to this group as it does not
permit binary attachments.



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