Re: ROM Dump of Amiga Keyboard controller

From: Jim Brain <>
Date: Fri, 18 Jul 2014 19:25:39 -0500
Message-ID: <>
On 7/18/2014 2:33 PM, Gerrit Heitsch wrote:
> As long as you do it in a way that the date is stable when the CPU 
> samples it (falling edge of its clock/PHI2 if I remember right), 
> everything will work and the exact timing is not relevant as long as 
> the time between command bytes is 2 periods of the external clock. So 
> safe points are rising and falling edge of 1, 3, 5 and falling edge of 
> 2 and 4. The rising edge of 2 and 4 would be the problematic part 
> where the data might not be stable. The safest way would be in the 
> middle of the HIGH or LOW portion of the external clock, that should 
> always work. Together with the rather slow clockspeed supplied (250 
> KHz external clock?), it should be stable at the sampling moment.
I chose 250kHz, knowing that the minimum was 100kHz internal (200kHz 
external), and I wanted a bit of a buffer.  I did try to slow the clock 
down, but it died slightly below 250kHz, so I think 250kHz is the 
effective minimum.


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Received on 2014-07-19 01:02:07

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