At 11:14 AM 11/14/97 -0800, you wrote:
>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

You can easily debug 2 PICs if you are using Picmasters. The software and
hardware allow up to 4 Picmasters to run at the same time. This gets a bit
expensive but in a bind it can be done. If you have a friend with a
picmaster you can sometimes persuade them to help you out and you use your
system and their picmaster to give you dual processor debug support.


Larry G. Nelson Sr.
mailto:L.Nelson@ieee.org
http://www.ultranet.com/~nr