1. Apr 2, 2012

### Teachme

Ok, so I am pretty sure I understand this Full Adder diagram fairly well. But I have one question... I included the picture of course.

Take a look at R5 1K. What is the purpose of this resistor? Why doesn't current always flow through the 1K R5 resistor rather than going to the 10K R6?

Also I highlighted to parts that I do not know what the symbols mean. The two triangles and the other triangle after R5.

I am assuming the first one completes the 5v circuit, but im not quite sure where the R5 resistor connects to.

Also here is a link to picture
http://www.waitingforfriday.com/images/e/e1/Logic_design_PNG.png [Broken]

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2. Apr 2, 2012

### rbj

wow, RTL. i haven't seen RTL since I was in school and i'm an old codger.

R5 and R13 are there to make sure Q3 and Q13 are "off" when they are meant to be. since very little current is required to drive Q4 and Q5, if R5 and R13 did not exist (were equal to $\infty \ \Omega$), then even if Q3 and Q13 were essentially off (barely conducting) Q4 and Q5 would be driven to "on" whether Q3 and Q13 were meant to be on or not.

3. Apr 3, 2012

### Teachme

Thanks a lot for the help! I really appreciate it. Makes much more sense now.

4. Apr 3, 2012

### Staff: Mentor

The 2 arrows circled: one is the emitter of the transistor symbol, and the end one is that lead going to ground, it's their ground symbol.