Re: Write only expansion register

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I'd thought about this while trying to optimise Greg\DAC's cartridge port
digimax.  Doing this would be just fine, but you need to be aware that
anything reading from the device will write bus noise to it.  If that's
acceptable, then there's no issue at all.

-David

On Mon, 6 May 2002 ncoplin@orbeng.com wrote:

> Hi all,
> 
> I'm experimenting with the concept of a wiring a write only register when
> the circuit board doesn't have access to the R/W signal (as with for example
> many CBM carts, or a single sided PCB).
> 
> My thinking is that with the appropriate IO select and Phi2 Clock it should
> be possible to get the latch (eg 74175) to accept the data. Logically
> NOR(NOT /IO2 OR CLOCK) for active low data.
> 
> Something like a 7400, 7402 or 74139 chip could decode this logic so that
> data available is latched at the negative edge of the clock.
> 
> Can someone verify if this would be so?
> 
> - Nick


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