Re: ROMs replacement.. solved!

From: Gerrit Heitsch <>
Date: Fri, 23 Nov 2012 18:53:44 +0100
Message-ID: <>
On 11/23/2012 06:43 PM, wrote:
> On 2012-11-23, at 18:30, Gerrit Heitsch wrote:
>>> I just had a look at the schematics of the narrow board and I wonder what the A14 is doing at the U4 (23128)..
>> Remember that BASIC ROM and KERNAL ROM in the C64 are not 'next' to each other. There is a 8 KB gap between them. So in order to select the correct 8 KB block in the 23128 ROM, you can't use A13. It would be HIGH at $A000-$BFFF and $E000-$FFFF. But you can use A14 since that is LOW at $A000-$BFFF and HIGH at $E000-$FFFF.
> That's clear but what I am wondering about is what do 15 address lines do at 16KiB ROM. And seem to be all connected. Or the guys just connected A14 from the bus to A13 of the ROM.. ? Have to check the 23128 pinout.
Yes, they left out A13. Meaning they connected A14 to the pin 'A13' at 
the ROM.


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Received on 2012-11-23 18:01:06

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