RE: PET 50Hz editor ROMS

I checked my files and I don't have 970150, but at some time I coppied 
the register values.  This was for a 9" PET which had the system board
replaced. The ROM was an EPROM, obviously with the CRTC programming 
patched.  This could also be used with an adapter to drive external 
monitors. The 50Hz PAL is probably for an external monitor, otherwise 
there is no reason to make it PAL compatible. In which case, monitor size 
doesn't matter.

The internal monitors use ramp generators for the horizontal sync. As 
long as the supplied sync rate is close, the monitor locks on. The 
registers on the CRTC are only one byte in length, limiting the accuracy 
of the resultant sync rate. The values chosen by the programmers provided
the desired appearance on the screen, knowing they could be a little off 
and still have it work. Remember, this is output from the CRTC, not input 
to the CRTC.


On Mon, 4 May 2015, Hoffmann-Vetter, Martin wrote:

>>            PET/CBM PET/CBM PET/CBM  8296D   NTSC     PAL
>>             60 Hz   50 Hz   50 Hz   50 HZ   60 Hz   50 Hz
>
>               12"     12"     12"     12"     9"?     9"?
>                                      other
>                                       crt
>
>> reg.  0     49      49      50      58      63      63
>
>> 324243             -01             -04
>> 901474     -03   -04-3681  -04                     -04_
>> 901498             -01
>> 901499     -01
>> 970150                                     -07
>
>> V. Lines   333     400     392     339     263     313
>> H. Dots    400     400     408     472     512     512
>> H. Sync.   19.98    20     19.6    16.95   15.78   15.65
>> Char. Rate 0.999     1     0.9996  1.00005 1.00992 1.0016
>> Dot Clock  7.992     8     7.9968  8.0004  8.07936 8.0128
>
> Where can i find the dump from 970150? Normaly this must be a version for 9"
> crt. For 9" you need 15.625 kHz horizonaly frequency. So the value from
> register 0 can be okay.
>
> You know, the first 9" crt needs 15.625 kHz for horizonal sync. (also used
> in the first PET without CRTC). The FAT 12" crt needs a higher horizonal
> sync. of 20 kHz for a higher voltage. The 12" crt from the 8296 needs only
> 17 kHz horizonal sync.
>
> All PET/CBM divided the dot clock from a 16 MHz crystal oscillator. Why do
> you have these value above?
>
> Martin
>
>
>       Message was sent through the cbm-hackers mailing list
>

wlevak@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org

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