Lpc2000

Barry,

Have you considered using standard 8-bit shift registers so that all you 
need is clock out and data in/out? If serial to parallel S/Rs such as 
the 74HC164 are used you can connect the outputs to the 16 lines and 
then feed the common (hopefully) back to the data line via a 10K 
resistor. That way you can ripple out a single active bit and then read 
it back on the data line as an input. Some gotchas are what if more than 
one output is active and this shorts a S/R output high to an active S/R 
output low etc. Ok, this shouldn't be a problem with the 12 position 
switch but could be with the keypad. But if you use the 4 keypad lines 
as the selects then the other 5 keypad lines can become inputs without 
conflict. Sound ok?

PORT EXPANDER using 74HC164 x 2 (daisy chained)
uP clk -> S/R clock
uP dat -> S/R data in
uP dat <- 10K resistor to switch common
S/R data x 4 -> keypad selects
S/R data x 12 -> 12 pos. switch.

my2cents
*Peter*

javida13 wrote:

> I have no need for the other parts in the family.  I need to read in
> 5-bits of a 5x4 keypad and 12-bits of a 12-position rotation switch
> (5+12=16).
>
> I'm using a Ramtron I2C memory device for my external memory
> requirements and RTC.  The part that I'm considering is a FM3164-S.  I
> just checked out the memory section and starting on the RTC.
>  
>