RE: Using large DRAM modules inside the C64

From: Baltissen, GJPAA (Ruud) (
Date: 2005-10-14 13:37:09


> 257 / 258?...
> > Sorry, it's indeed a dual 4-to-1 multiplexer and not a quad 2-to-1,
> > as I thought.

I need a 1-to-2 demultiplexer and then every input must be set seperately. I
think it simply doesn't exist and found out that the next easiest way is to
take two 74LS139 who can provide the four 'elements' I need.

Where do I need it for? The idea is to enable the user to choose between the
original ROM or a replacement RAM. The original input towards the ROM is fed
to the 139 and an output from a 6526 decides whether the original ROM is
selected or RAM. The RAM can be written and read by a 65816 in the $FFxxxx

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