# Creating truth table

I want to create a truth table to see all options for 74HC123 output. Basically an optocoupler output is connected to 74HC123 as input. 74HC123 will get the data from optocoupler. There could be two options "0" and "1".

Optocouple has 1 output and 74HC123 has 3 inputs. So i wanted to create truth table to see options for output data.

I did something like this:

74HC123 truth table:

Is it true? If it is wrong, how can i do it?

• If you compare your table to datasheet table, they don't match. Just use datasheet table. Mar 25 at 9:14
• @Justme what's wrong with mine ? All i did was giving nA,nB and nRD "0" and "1". Mar 25 at 10:13
• That is exactly the problem. The chip does nothing interesting when inputs are stable, i.e. not changing. The datasheet table shows how the chip reacts to changing inputs. Mar 25 at 10:23
• @Justme Can you please give me an example about part of changing and not changing inputs? Mar 25 at 11:01
• $\uparrow$ is an example of a changing input: LOW-to-HIGH transition. For this you have to consider the previous and current state of the signal.
– Seir
Mar 25 at 11:06