Re: Hardware emulation of 6509 using 6502?

From: Jim Brain <brain_at_jbrain.com>
Date: Sat, 24 Feb 2018 21:39:44 -0600
Message-ID: <7d0542f1-1d8c-08cb-b595-9c10e860e80d@jbrain.com>
On 2/24/2018 9:19 PM, Dr Jefyll wrote:
> Dr Jefyll wrote
>> We can't have
>> read data from memory at $0000 or $0001 /also/ attempting to drive the
>> bus.
> Huh -- or maybe we CAN!  The question is, are /writes/ to $0000 and $0001
> also passed on to RAM? With the present arrangement I think they are. That
> means it's OK to have two bus masters later when the read occurs, because
> the data will be the same!
I was going to response earlier.  I don't think it is a problem.

If there is no RAM at 0/1, then the CPLD owns the bus.
If there is RAM at 0/1, then the CPLD and the RAM will both own the bus, 
but there will be not a major problem,

The only issue is if there is ROM at 0/1
>
> But is the present arrangement acceptable? I heard some discussion somewhere
> about writes to $0000 and $0001 /not/ being passed on to RAM. Is that a
> desirable thing? Here's where my lack of CBM knowledge becomes apparent...
This is an issue with the 6510, where the parts are truly internal, and 
no external write is asserted
> :o/
>
> cheers,
> J
>
>
>
> --
> Sent from: http://cbm-hackers.2304266.n4.nabble.com/
>
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-- 
Jim Brain
brain@jbrain.com
www.jbrain.com


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Received on 2018-02-25 06:00:24

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