New subject: Address Decoding for Dummies! (was: SPDT Dip Switches...

15 Sep 2001

On Sep 15, 14:42, Roger Merchberger wrote:

...
  My idea: A 2-4 decoder/demux. tied to A0 & A1,
with the outputs going to
 one side of a SPDT DIP switch, the other side of the switch pulled to +5,
 then all four of the switch outputs going into a 4-input AND gate. That
 way, you could switch any of the four addresses on or off, so that you'd
 have access to more than one memory location for CE/ to implement UARTS &
 stuff that require more than one address to function. (It can be done
 easily without the switches -- I could use a jumper block without
 heartburn, but the switches would look neater, and wouldn't have the chance
...
  for floating inputs/outputs...) 
In other words, this:

                                                _____
                          ____ +5V         - ---|    \
            _____          |               - ---|  &  \_____
           |     |__ _     o               - ---|     /
  A0 ------|  2  |__ _     ----o----------------|____/
           |  to |__ _     o
  A1 ------|  4  |_________|
           |_____|

Wouldn't this be easier and do the same thing?

				  ____ +5V
				   |
                           	   \  4 x 1k0 pullup
                                   /	  	_____
            _____                  \	   - ---|    \
           |     |__ _             /	   - ---|  &  \_____
  A0 ------|  2  |__ _     	   |	   - ---|     /
           |  to |__ _     ----o----------------|____/
  A1 ------|  4  |_________o
           |_____|

I've just seen Tony's reply, and his suggestion using a MUX would have been
my next suggestion too.  It's also easier to extend to more address bits
(fewer switches required).

-- 
Pete						Peter Turnbull
						Network Manager
						University of York

SPDT Dip Switches (was: Solomon Splitting the list...