Hello, here is my task:
TTL circuit is connected to data bus. Determine if operation of circuit is disturbed. It is known:
RB = RB' = RB'' = 4K Ohm, RC2 = RC2'= RC2'' = 1.6K Ohm, RC4 = RC4' = RC4'' = 130 Ohm, RE2 = RE2' = RE2'' = 1K Ohm,
Vcc = 5V, Vces = 0.2V, Vbe = 0.7V, Vbes = 0.8V, Bf = 20, Br = 0.1. Output of Circuit 1 is low, output of Circuit 2 is high and
output of Circuit 3 is high.


So here we have 3 NAND gates with outputs connected together.



It is obvious that we have conflict situation here. What calculations look like for this situation?

 

Hello,

For connecting TTL to a bus, there are special bus recivers like the 74245:



Bertus

 

Hello, thanks for reply.
I'm aware that basic TTL circuits can't be connected to data bus (for that purpose there are tristate TTL circuits) but this is homework question and they want me to prove this mathematically...

 

You can analyze the circuit to determine what, given the simple transistor models you are working with, the voltage on the bus will be. It's a pretty straightforward circuit.

But first consider what the value SHOULD be. If you can't determine that, then it really doesn't matter what the circuit actually does since what it should do isn't even defined.