Hi to you all

My question has to do with a project in which I got involved as is something like this:

There are 4 pcf8574, each takes care of 8 micro-switches (with pull-up resistors) each micro-switch senses the presence (or not) of a product over it.

So, with the product over the micro-switch the pcf reads a "zero" (and assumes there is a product), without the product it reads a "one".

If for any reason I disconnect (or it became dammaged) one of the boards that has a pcf8574, when I tell the PIC to read the bus it sees the absent pcf8574 as having all the inputs with "zeros".

Can anyone sugest a way to check if there is really a pcf on the I2C bus or I'm seeig a ghost pcf.

Thanks in advance.

Thanks Lester for this comunication thread, hope everybody follow these new rules