Why use pullup resistors?
This way, if the pins get set to an unintended state (due to software bugs or electrical noise or whatever), the chip will not be damaged because the current will be limited by the resistor. When using pullup (or pulldown) resistors, the worst that can happen is accidentally driving an output against a pull up/down and thus wasting power. (See “power considerations” section below). • having a resistor on all unused inputs facilitates testing. Even if the gate has no effect on whether the product will work or not, companies like to run the standard test routine for testing each part on their ICT (in-circuit tester), so the ability to drive all inputs to an arbitrary state is needed. • makes temporary changes easier during test and debug as the resistor can be over-ridden easily with out removal. • The cost of the resister is minimal to beginning projects. I have found that the last minute design change or feature addition is the rule rather than the exception. I ALWAYS allocate space to
