Re: PET 50Hz editor ROMS

Remember, on the 80 column machines the pixel clock is doubled, so even with the same registers the "H" resolution is also doubled.

Steve
 

________________________________
 From: William Levak <wlevak@SDF.ORG>
To: cbm-hackers@musoftware.de 
Sent: Wednesday, April 30, 2014 12:45:57 AM
Subject: Re: PET 50Hz editor ROMS
  

On Sun, 27 Apr 2014, Rob Clarke
 wrote:

> OK, here's a text version. The xls contains the formulas for working out the 
> frequencies and frame rates. How about an open format like ODS, will that do?
>
> http://inchocks.co.uk/commodore/PET/PET_CRTC.csv

That makes it clear.  For the 60 Hz versions, the 40 and 80 column ROMs 
use the same CRTC values.  The 50 Hz versions have different CRTC values 
for the 40 and 80 column versions.  There is also a PAL version.  That 
makes 4 different sets of CRTC values.

I have calculated the screen resolution for these values, and the area 
of the screen actually used.

Resolution:
  H = (R0+1)x8 + (R2+1) + R3
  V = (R4+1)x(R9+1) + (R7+1)

Area Used:
  H = R1x8
  V = R6x(R9+1)

                Resolution 
 Area Used
                  H x V       H x V
         60 Hz  457 x 360   320 x 250
                457 x 362   320 x 200
40 col. 50 Hz  457 x 400   320 x 250
                457 x 438   320 x 200
80 col. 50 Hz  457 x 423   320 x 250
                457 x 430   320 x 200
80 col. PAL    571 x 329   320 x 225
                571 x 329   320 x 200

That still leaves four variations of the 40 column 50 Hz ROMs.  The 
keyboard scan table is also in these ROMs.  We would need to know what 
language each ROM supports in order to uniquely identify them.


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

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