Re: DRAM refresh

From: Hegedűs István <>
Date: Fri, 14 Oct 2016 12:20:24 +0200
Message-ID: <>

Yes. It was a surprise for me also. Indeed it rolls over inside the visible 
screen area several times, however there is a forced clear in scan line 0 
thus the refresh is uneven. Some rows get more refresh.

-----Original Message----- 
From: Gerrit Heitsch
Sent: Friday, October 14, 2016 8:26 AM
Subject: 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.


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Received on 2016-10-14 11:01:03

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