Re: DRAM refresh

On 10/13/2016 11:10 PM, Hegedűs István wrote:
> Hi,
>
> I have played a lot with TED's refresh counter. The counter's enable
> signal is maintained by a latch which is triggered by the horizontal
> counter at position 296. Horizontal position 336 clears this enable signal.
> Playing with hcounter and setting the right value at the right time I
> have managed to bypass this clear signal but the refresh single clock
> signal ended normally (single clock change is triggered by different
> hcounter value). The result was that refresh counter stayed on and
> counted while the CPU was running already on double clock. This way I
> have managed to identify that TED clears the refresh counter at
> horizontal position 431 when the scanline is 0 (or the refresh counting
> has stayed on by manipulation or TED stop bit is active).

You mean that the refresh counter is cleared at a certain position 
instead of just rolling over? I wonder why they did that since it will 
produce an uneven refresh.

  Gerrit



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