Rob Bristow wrote:
>
> Hi
>
> I am looking for a way to multiplex the port pins on the PIC16C73A.
> I currently require a further 5 input pins and further 8 output pins.
> This is after having used up most of the pins available on my micro.

I posted a similar message last month, and got a number of useful
replies - to summarize the most popular ones:

(1) using a shift register latch (e.g. 74HC595).
(2) addressable 8-bit latch (e.g. 74HC259).
(3) using a decoder (e.g. 74HC138) feeding multiple latches for output
(e.g. 74HC574) and tri-state buffers for input (e.g. 74HC541).
(4) using a decoder for 1-of-N outputs (e.g. 74HC154, 74HC138 or 4028).

In the end I just used a 4028.  However, there's one option that
I didn't consider at the time - adding another PIC.  This would have
almost doubled the number of pins (need 2 pins each to communicate).
Some pros and cons:

- PICs usually cost more than logic chips
+ You'll use double the number of PICs, so get volume breaks
+ No source problems (ha!)
+ Configuration is completely soft
+ You can swap PICs between circuits when prototyping
+ You get double the processing power; useful for me because I wanted
real-time audio playback _and_ an interrupt-driven clock.  Hard to do
with just 1 16C84.
- Hard to debug 2 PICs simultaneously

James.