Re: 264 series questions

From: Marko Mäkelä (
Date: 1999-10-04 13:36:02

On Mon, 4 Oct 1999, Nicolas Welte wrote:

> BTW, how do the TED memory accesses work?

When I got my C16 a couple of years ago, the first program I wrote for it
was a memory access logger (similar to the ones for the C64 developed by
Andreas Boose and me, but much simpler, thanks to the "horizontal raster
position" register of the TED).  I don't think that I ever released the 
results to the public, though; I just mailed it to a few plus/4 freaks.

One interesting thing, found by Levente (I think), is that memory
refreshes are like reads from $FF00-$FFFF.  When the refresh was at
$FF00-$FF3F, the program recorded the corresponding TED register values
(although it was reading from the same constant address in open address
space all the time).

> it must have more accesses to the memory than the VIC-II.

True, it has two bad lines, one 1 line before the character row and one at
the first line of the character row.

> It should also be true that the TED memory clock always runs at about
> 2MHz and uses

Yes, and the CPU will automatically be switched to single clock when the
TED needs the bus.  I'm not aware of any way to override that, to get a
result similar to that on the C128, where the VIC-IIe will happily display
data fetched by the processor.


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