Re: Dating a C-64 board

From: Marko Mäkelä (
Date: 1999-04-18 20:07:25

On Sun, 18 Apr 1999, Ethan Dicks wrote:

> > The NTSC VIC-20 runs at the same speed at the NTSC C64...
> I don't think that's correct.  In my original 1541 manual, it mentions the
> U+ and U- commands to change the IEEE speed to match VIC-20 or C-64 speeds.

Aren't they UI- and UI+?  Anyway, Richard is correct.  The reason why
those commands were introduced is that the C64 has bad lines (video DMA
that will occasionally interrupt the processor) while the VIC-20 does not.  
If you blank the screen of an NTSC C64, it will run at the same speed as
an NTSC VIC-20.


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