Re: C64 MMU POC

From: smf <smf_at_null.net>
Date: Wed, 10 Jul 2019 22:41:54 +0100
Message-ID: <e8e0e09d-1df2-9022-c393-fbf9b75d6d4e_at_null.net>
There was also a real time clock chip that only required a free rom
socket, to set the time you treated some of the address bits as data.

On 10/07/2019 17:09, André Fachat wrote:
>
>
> Am 10. Juli 2019 17:51:00 schrieb laughton_at_cyg.net
>>
>>
>> Interesting...  So, you'd read several bytes whose value you actually
>> don't care about...  but the decoder hardware would recognize *which*
>> bytes you'd read; and, from that, infer what MMU operation you wanted?
>
> Yeah. I used this technique to implement IO ports on the Atari ST ROM
> port :-)
>
> Just used a 256 byte address range and used the lower 8 address bits as
> output value when an address in that block was read
>
> This way my Atari ST became an IEEE488 connected harddisk for my C64 :-)
>
> André
>
>>
>>
>> cheers
>> J
>>
>>
>>> and think about very unlikely
>>> read sequences that won't be triggered by random register accesses.
>>> Of course, with this method, such a register can't be read by the cpu.
>>>
>>>
>>>
>>>
>>> Frank
>
>
>
>
Received on 2020-05-29 22:30:05

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