Re: BASIC and System ROM replacements

From: Gerrit Heitsch <>
Date: Thu, 30 May 2013 08:55:15 +0200
Message-ID: <>
On 05/30/2013 08:22 AM, Jim Brain wrote:
> Speaking (writing) of bank registers, anyone know of a TTL option that
> has a falling edge trigger?  Yes, I can do an inverter, but would rather
> not.  Use case is VIC-20, which won't work on rising edge of Phi,
> because not all of the data is valid on rising edge.

The 74LS373 or 74LS573 does that. But it's a latch, not a register. They 
use it in the C64 to de-multiplex the VIC address so it can access the 
char ROM. Trigger is the falling edge of _RAS.

Now you have to check if a latch works in your case.


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Received on 2013-05-30 07:00:52

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