Weird pulses on KERNAL chip select line

From: Michał Pleban <>
Date: Sun, 26 May 2013 21:59:04 +0200
Message-ID: <>

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

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.


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Received on 2013-05-26 20:03:45

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