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VBL duration?

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  VBL duration? Egan Ford <datajerk@gmail.com> - 2012-06-27 08:40 -0600
    Re: VBL duration? Vladimir Ivanov <vladitx@XXXyahooXXX.com> - 2012-06-28 09:58 +0300
    Re: VBL duration? aiiadict@gmail.com - 2012-06-28 06:59 -0700
      Re: VBL duration? Egan Ford <datajerk@gmail.com> - 2012-06-28 09:48 -0600
        Re: VBL duration? Gary Gray <vengefultacos@gmail.com> - 2012-06-29 17:10 -0400
          Re: VBL duration? aiiadict@gmail.com - 2012-06-29 15:58 -0700
            Re: VBL duration? aiiadict@gmail.com - 2012-06-29 16:00 -0700

#310 — VBL duration?

Programmers,

For an NTSC IIe what is the duration of the vertical blanking interval?

Thanks.

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#311

On Wed, 27 Jun 2012, Egan Ford wrote:

> For an NTSC IIe what is the duration of the vertical blanking interval?

70 lines.

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#312

http://rich12345.tripod.com/aiivideo/vbl.html

On Wednesday, June 27, 2012 7:40:19 AM UTC-7, datajerk wrote:
> Programmers,
> 
> For an NTSC IIe what is the duration of the vertical blanking interval?
> 
> Thanks.

http://rich12345.tripod.com/aiivideo/vbl.html


70 scanlines * 65 cycles = 4550 cpu cycles


Rich

On Wednesday, June 27, 2012 7:40:19 AM UTC-7, datajerk wrote:
> Programmers,
> 
> For an NTSC IIe what is the duration of the vertical blanking interval?
> 
> Thanks.

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#313

On 6/28/12 7:59 AM, aiiadict@gmail.com wrote:
> http://rich12345.tripod.com/aiivideo/vbl.html
>
> On Wednesday, June 27, 2012 7:40:19 AM UTC-7, datajerk wrote:
>> Programmers,
>>
>> For an NTSC IIe what is the duration of the vertical blanking interval?
>>
>> Thanks.
>
> http://rich12345.tripod.com/aiivideo/vbl.html
>
>
> 70 scanlines * 65 cycles = 4550 cpu cycles
>
>
> Rich
>
> On Wednesday, June 27, 2012 7:40:19 AM UTC-7, datajerk wrote:
>> Programmers,
>>
>> For an NTSC IIe what is the duration of the vertical blanking interval?
>>
>> Thanks.
>

Thanks guys.  Rich, great links.  Thanks.

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#315

Inside the //e has a program in it that you can run to determine how 
long the VBL is:


"If you load this program into mem-
ory and then enter CALL 768 to activate it, a  number will be dis-
played that should be either 520 or 521. This number is equal to
the  number of 24  machine-cycle  periods  that  occur  during  one
vertical blanking interval. Thus, the vertical blanking interval is
somewhere between 12,480 and 12,504 machine cycles."



On 6/28/2012 11:48 AM, Egan Ford wrote:
> On 6/28/12 7:59 AM, aiiadict@gmail.com wrote:
>> http://rich12345.tripod.com/aiivideo/vbl.html
>>
>> On Wednesday, June 27, 2012 7:40:19 AM UTC-7, datajerk wrote:
>>> Programmers,
>>>
>>> For an NTSC IIe what is the duration of the vertical blanking interval?
>>>
>>> Thanks.
>>
>> http://rich12345.tripod.com/aiivideo/vbl.html
>>
>>
>> 70 scanlines * 65 cycles = 4550 cpu cycles
>>
>>
>> Rich
>>
>> On Wednesday, June 27, 2012 7:40:19 AM UTC-7, datajerk wrote:
>>> Programmers,
>>>
>>> For an NTSC IIe what is the duration of the vertical blanking interval?
>>>
>>> Thanks.
>>
>
> Thanks guys. Rich, great links. Thanks.
>

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#316

On Friday, June 29, 2012 2:10:15 PM UTC-7, Gary wrote:
>  Thus, the vertical blanking interval is
> somewhere between 12,480 and 12,504 machine cycles."
> 


http://rich12345.tripod.com/aiivideo/vbl.html


the video screen takes 12,480 cycles to update.  This
includes time to "horizontal blank" and display video
data.


it works like this, starting from edge of VBL=true
to VBL=false

ScanlineX
Draw Scanline #1, 40 bytes of video data, 1 cycle for
each byte

do "scanline #1" "horizontal blank", 25 cycles.  This 
moves the electron gun down to Scanline #2.

if not done with all scanlines, goto ScanlineX (above)

VBL= TRUE.  The electron gun is moving back up to the
upper left of the screen, from the lower right.

VBL lasts for 4550 cycles.  Repeat

http://rich12345.tripod.com/aiivideo/softalk.html

includes a trick to see what line is being scanned
by video circuits, by putting known data in video
RAM, and then reading floating bus to see if this
data is currently on it.

there are a few games that use this as a trick
to inter-mix graphics modes.

There was a discussion about apple II video,
floating bus on comp.sys.apple2 within the last
year that included a floating bus test that would
verify if an emulator properly emulated the video
generator of the apple II.

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#317

On Friday, June 29, 2012 3:58:48 PM UTC-7, (unknown) wrote:
> 
> it works like this, starting from edge of VBL=true
> to VBL=false
> 

the transition from true to false, IE the end of
VBL

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