Re: Hardware emulation of 6509 using 6502?

From: Segher Boessenkool <*segher_at_kernel.crashing.org*> Date: Sun, 25 Feb 2018 13:04:23 -0600 Message-ID: <20180225190423.GN21977@gate.crashing.org> · segher_at_kernel.crashing.org

On Sun, Feb 25, 2018 at 12:36:49PM +0000, smf wrote:
> On 25/02/2018 10:17, Segher Boessenkool wrote:
> >All 6510 accesses to 0000/0001 are done on the external bus (the read
> >result just never is used).

> According to
> 
> http://codebase64.org/doku.php?id=base:ram_beneath_00_and_01
> 
> The 6510 doesn't drive the data bus when writing to $00 or $01, so you 
> get what was last read by vic 2
> 
> There is a test program which verifies this 
> https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/general/ram0001/

Oh, hrm, I misremember that detail then, sorry.  It does make sense yes;
it just forces DBE low internally.

Segher

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