RE: decoding address
Date: 2002-10-02 18:07:36

On Wed, 02 Oct 2002 03:04:20 -0700 wrote:
>Hallo John,
>> Back in the old days, you'd use something like the 74LS682.  
>or 688
Ok I found it, it's exactly the chip I described that I wished I had, cool!
The SN54/74LS682, 684, 688 are 8-bit magnitude comparators. These
device types are designed to perform comparisons between two eight-bit
binary or BCD words. All device types provide P = Q outputs and the LS682
and LS684 have P>Q outputs also.

basically if the two 8bit numbers match, the q goes low.  The other versions can do greater than as well.  You could combine those of course for >= and <.  So to answer my question,  when both i/o1 and q are low your at the decoded address at $de00.  But this is just a pulse and you would need a flipflop to toggle the LED on/off.  Cool, I should try making it.. I think people could find some uses for this simple circuit.. of course with the user port this example is pointless right now.  But you could add a chip like an ADC or ram and stuff.

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