Re: Microcontroller "PEEKing" into C64 memory?

From: Gerrit Heitsch <>
Date: Thu, 21 Jan 2016 21:41:14 +0100
Message-ID: <>
On 01/21/2016 09:33 PM, wrote:
>> On 2016-01-21, at 21:18, wrote:
>>>>> If what you need is mirroring of a portion of C64 ram I have a FIFO
>>>>> based bus snooping design that could work, but I haven't had a chance to
>>>>> verify it.
>>>> I'd also be interested in a design, as I have a few ideas that need such
>>>> an integration.  I had been planning to implement 8 registers in a CPLD
>>>> with dual port access, but maybe there are better ways to do this...
>>> How do CPU carts access the RAM? I mean how the external CPUs do it from the
>>> EXPANSION port.
>> using the DMA line (which halts the internal CPU and removes it from the bus)
> Well, that's what I mean - if all what's needed is to peek a few bytes off some location from time to time? Or is it supposed to be completely invisible to the system?

Remember that VIC will still use the bus though, only the CPU is taken 
offline with the DMA line! So you have only about 500ns time before you 
need to free the bus again.


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Received on 2016-01-21 21:04:11

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