Cycle and video timings

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Xeron
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Cycle and video timings

Post by Xeron » Sun Mar 08, 2009 11:12 pm

I have some questions about timings in the Oric-1 and Atmos.

Where there NTSC models ever released, or just PAL?

When you set 60Hz mode, i presume thats a 60Hz PAL signal, rather than NTSC?

How many CPU cycles are executed per raster line?

Of the 312 PAL raster lines, on which line does the Oric start/stop drawing video?

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Re: Cycle and video timings

Post by JamesD » Sun Mar 08, 2009 11:31 pm

Xeron wrote:I have some questions about timings in the Oric-1 and Atmos.

Where there NTSC models ever released, or just PAL?

When you set 60Hz mode, i presume thats a 60Hz PAL signal, rather than NTSC?

How many CPU cycles are executed per raster line?

Of the 312 PAL raster lines, on which line does the Oric start/stop drawing video?
No NTSC machines were released.

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Xeron
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Post by Xeron » Mon Mar 09, 2009 5:19 pm

OK, thanks.

Anyone know the other answers?

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Dbug
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Re: Cycle and video timings

Post by Dbug » Mon Mar 09, 2009 7:50 pm

Xeron wrote:When you set 60Hz mode, i presume thats a 60Hz PAL signal, rather than NTSC?
Yup, PAL 60
Xeron wrote:How many CPU cycles are executed per raster line?
About 64 cycles at 50hz.
Xeron wrote:Of the 312 PAL raster lines, on which line does the Oric start/stop drawing video?
No idea, but this can be figured out by testing the value of the sync line on the socket.

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Re: Cycle and video timings

Post by JamesD » Sun May 24, 2009 4:49 pm

Xeron wrote:How many CPU cycles are executed per raster line?
About 64 cycles at 50hz.

Did the display steal that many clock cycles during the display update?
I mean... 1 MHz vs 50 Hz?

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Dbug
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Re: Cycle and video timings

Post by Dbug » Sun May 24, 2009 4:58 pm

JamesD wrote:
Xeron wrote:How many CPU cycles are executed per raster line?
About 64 cycles at 50hz.

Did the display steal that many clock cycles during the display update?
I mean... 1 MHz vs 50 Hz?
well, 1mhz=1000000hz

1000000/50=20000 cycles per VBL
20000/~312=64 cycles

Don't see what is stolen :)

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Re: Cycle and video timings

Post by JamesD » Sun May 24, 2009 5:48 pm

Dbug wrote:
JamesD wrote:
Xeron wrote:How many CPU cycles are executed per raster line?
About 64 cycles at 50hz.

Did the display steal that many clock cycles during the display update?
I mean... 1 MHz vs 50 Hz?
well, 1mhz=1000000hz

1000000/50=20000 cycles per VBL
20000/~312=64 cycles

Don't see what is stolen :)
Ah, PAL raster lines. That's why it looked off. I was still thinking NTSC.

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