Re: ROM Dump of Amiga Keyboard controller

From: Jim Brain <>
Date: Fri, 18 Jul 2014 19:18:09 -0500
Message-ID: <>
On 7/18/2014 1:41 PM, Gerrit Heitsch wrote:
> To remedy that you need a command sequence that makes sure a certain 
> Byte WILL be executed as a command, from then on you know the internal 
> state of the CPU and it becomes easy. That's what I supplied with the 
> BIT command. Since with a long enough sequence of NOPs, there are only 
> 2 alternatives, it will be either the first or the second:
> EA EA EA EA 24 EA EA A9 00
> ex -- ex -- ex -- -- ex --
> -- ex -- ex -- ex -- ex --
> Either way, A9 will be executed as command and the accu will be loaded 
> with #$00.

Yes, I want to call this out.  This was the other piece that made me 
more confident that success could be achieved.  I think this, coupled 
with Greg's suggestion, made the solution clear to me.
> The other thing I remember was that the 6500/1 does divide the 
> externally supplied clock by two. But the longer I think about it, the 
> less I see that as a problem as long as you feed the bytes at the 
> right speed (meaning half the clockspeed), the clock phase is of no 
> consequence as long as the data read by the CPU is stable the moment 
> it's sampled.
Yep, I agree.  I saw your concern, but I figured just leaving the data 
there for both cycles would ensure success.


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Received on 2014-07-19 01:01:09

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