Re: ROMs replacement

From: Spiro Trikaliotis <ml-cbmhackers_at_trikaliotis.net>
Date: Mon, 17 Sep 2012 20:00:33 +0200
Message-ID: <20120917180033.GO12722@trikaliotis.net>
Hello,

* On Mon, Sep 17, 2012 at 07:00:45PM +0200 Gerrit Heitsch wrote:
 
> You will also need the '245 to give the 6502 the ability to tristate
> the address lines. Not sure if you really need the '245 for the data
> lines, I thought those are tristate in the 6502 already, but it
> can't hurt.

They are not really tristate in the 6502. If it reads, however, then the
data lines are not driven, they only sink current. That might be enough
if you can guarantee the 6502 is only reading while the 6569 access the
RAM. (Can you?)

If -RDY is high (and after the 3 clock cycles one has to wait), this is
true. I am not sure about the VIC access with PHI2=0, if the 6502 is
just writing data. I believe R/W should be 1 then, but I am not
completely sure if this can be guaranteed.

Regards,
Spiro.

-- 
Spiro R. Trikaliotis
http://www.trikaliotis.net/

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