Re: Weird pulses on KERNAL chip select line

From: Gerrit Heitsch <>
Date: Mon, 27 May 2013 16:53:17 +0200
Message-ID: <>
On 05/26/2013 09:59 PM, Michał Pleban wrote:
> Hello!
> Today I noticed something strange with the KERNAL /CS line of the C64.
> Normally this line should go low only when KERNAL is accessed. But I am
> seeing very short low pulses (about 50ns) at the beginning of many clock
> cycles.
> These pulses mess up with my Flash handling circuit so I need to get rid
> of them. I thought of a simple RC filter for this purpose, but my first
> question is why they occur at all? Is that some artifact which happens
> when the VIC handles the bus back to the CPU? There is no such
> phenomenon on respective CS lines of BASIC and CHAROM.

You should look again. Especially the _CS line for the Char-ROM does 
have many strange things happen on it.


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Received on 2013-05-27 15:00:04

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