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Date Posted: 16:06:05 02/19/02 Tue
Author: Potter
Subject: Re: Blanking durring VBI
In reply to: Jain 's message, "Re: Blanking durring VBI" on 06:00:30 02/18/02 Mon

What I did: the flag VIDEOKAY is intended to disable descrambling if the video is interpreted as bad and it simply passes straight through untouched (apart from clamping) so I found a way to discrimate normal video and forced this flag to be reset even if the the code managed to lock. Descrambling won't start until 4 good frames are passed anyway so the flag only has to be reset every 2-3 frames to prevent descrambling from starting. The simplest way of doing this (if all else fails) is wire a SPST toggle switch to a spare port input with a pullup resistor and add some lines to SETMODE
#define mansw porta,3 ;example switch on RA3 (pin2)

btfss mansw ;switch on?
bcf videokay ;y - force flag to bad

remembering to use the appropriate labels for whatever version of code you're using and also remember to deduct 2 cycles from the big wait at the end of SETMODE to maintain the existing timing.


>In my previous message, read: "...(I mean output
>"Normal" in 1 all the time for unscrambled channels)"
>J
>>Hi
>>That sounds like a fairly easy change - to get the pic
>>to pass the actual signal instead of inserting black
>>on non-visible lines. In MAINLOOP a flag is set for
>>MAKEHLINE to create black on the non-visible lines
>>(PASSBLACK) and it's reset at the start of the visible
>>lines. In MAKEHLINE at the end of the burst period
>>this flag is checked and if set it causes an
>>artificial black to be inserted something like this:
>> movlw VIDEOOUT
>> btfsc VIDSMODE,DOINVERT ; IF we have to invert
>> movlw INVERTIT ; make invert
>> btfsc VIDSMODE,PASBLACK ; IF we have to make
>>black
>> movlw BLACKOUT ; make BLACK ****HERE****
>> btfss VIDSMODE,VIDEOKAY ; IF not decoding
>> movlw VIDEOOUT ; just pass video
>> movwf PORTB ; ACTIVE VIDEO LINE BEGINS
>>If you change the movlw BLACKOUT to movlw VIDEOOUT the
>>actual black level will pass but includes all
>>extraneous data on the signal as well (data packets,
>>teletext, macrovision, noise etc etc). Sync
>>regeneration and burst handling are not affected and
>>MAKEVBI will still insert artificial black unless the
>>same change is made in there as well. Individual
>>lines may be handled differently by expanding MAINLOOP
>>and setting the flags however you need.
>>PS after looking at my coding (lost in the codewoods)
>>it may be that what I decribed to you earlier was
>>wrong and I'm not sampling a true black level after
>>all as that was an earlier incarnation - more late
>>nights to come.
>>
>>
>>>Is there any code (for NTSC) that doesn't put
>blanking
>>>pulse from PIC in 1 durring VBI (but only durring
>>>synchro part of the line, including VBI)?
>>>Jain

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