Re: Some new 8032 Editor/Char roms

From: Marko Mäkelä <>
Date: Sat, 25 Apr 2015 10:20:48 +0300
Message-ID: <20150425072048.GA2137@x220>
On Fri, Apr 24, 2015 at 10:50:12PM +0200, wrote:
>well, yes, that is correct - however, that only means the TOD clock of 
>the CIA (if any) needs different initialization.

There is no MOS 6526 CIA in the PET. IIRC, the PETs use two MOS 6522 
VIAs (like the VIC-20) and one MOS 6520 PIA.

Even in the Commodore 64, as far as I remember, the 50/60Hz TOD flags in 
the two MOS 6526 are not initialized differently. The first C64 KERNAL 
version did not even bother to check for PAL/NTSC. Later ones do, IIRC 
by waiting the raster counter register at $d011/$d012 to wrap around or 
reach a particular line. The result of this check is written to some 
location in the $2xx page, but IIRC it does not affect the operation of 

On the PET, I would expect the 6545/6845 CRTC registers to have to be 
initialized differently for 50Hz and 60Hz timings. I never played with 
the CRTC registers on the PET, so I do not have first-hand experience.  
But, if the processor and peripherals cannot detect if the hardware is 
on 50Hz or 60Hz, it would seem to me that the timings should be 
hard-wired in the editor ROMs, just like in the later Commodore 264 
series where the TED chip can output PAL or NTSC, depending on the 
register settings (and the color clock crystal frequency).


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Received on 2015-04-25 08:00:05

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