15 Sep
2001
15 Sep
'01
11:30 a.m.
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