Ok, here is the situation. in my alarm project, I have several Arduino's for different tasks, and rather than opening up the enclosure to program the modules, I would like one plug socket on the front of the enclosure, (behind a locked panel), select the module via something, possibly just a rotary switch to select the reset line of the module, and upload the code. can this be done? I assume yes but I wanted to be sure before I toasted something.
I am just trying to simplify debugging my alarm system as I build it.
I know I will have to pull the power source jumper on my programmer so there are no PSU conflicts.
Obviously, a rotary switch is rather old-school, but I wasn't sure what else would be low tech, and bug free.
Yes if any of them are using SPI you are in trouble.
Better think of another way For example you could make some hardware to MUX the signals, the question is "Is it worth it?"
Another option could be to write a custom bootloader that loads from a UART or I2C or even a couple of spare pins maybe and have a method to select the active Arduino.
Once again, is it worth it? Maybe if you will be making a lot of changes over a long period.
the ICSP port is nothing more than an SPI interface,
The ICSP includes control over the processors reset, something the SPI does not need. So you can't upload anything while code is running.
and if I use THIS, I can up to 16 arduino's from one port,
That only controls one signal line.
The problem with trying to do what you want is that you would have several outputs connected together.