pullup/down or not at all

mobile_bob

Guys:

i am working on a project that connects two bs2 stamps in series by one to· 5 pins

basically the last in line is sitting in loop scanning an input pin waiting for a high logic to come in, so that it can start its
routine.

the stamp connected to this pin is already doing its thing and sets and output to high when it wants the second bs2 to start or break out of its loop

my question is
when connecting two bs2's together do i really need pullup or pull down resistors? if so why?

thank you

bob g

Mike Green

You should have one or the other (pullups or pulldowns). The issue is that, when the Stamps are reset, the I/O pins are all in the input mode which means that their state is indeterminate. It can be affected by static electricity, by capacitance effects, the phase of the moon, etc. until one of the Stamps sets its pin to output mode. The pullup or pulldown provides a known state.

Also, if the I/O pin is "drifting" and the voltage on the pin is near the switching threshold, the current consumption of the input circuitry will rise which is a problem if you're running things off batteries for extended periods of time.