1. The problem statement, all variables and given/known data 8. Describe why rails are used in building a digital logic circuit. 9. Describe why a pull down resistor is needed for a switch in a digital circuit. 2. Relevant equations 8. I've found nothing on rails. 9. A resistor with one end connected to a LOW voltage level and the other end connected to an input or output line so that when that line is in the float condition (not HIGH or LOW), the voltage level on that line will, instead, be pulled down to a LOW state. 3. The attempt at a solution I don't know enough about such architecture to approach this.