Student "edition" found at {csi dot journalspace dot com}.

Maybe I shouldn't have started this blog now, not with everything that's been going on.

In the second session of my Computer Systems Organization lecture class for the ninth week of the third term, I started the discussion of flip-flops.

This is a strange kind of circuit that is not computational or sequential like all of the others we have taken up, where the outputs are dependent only on the input or inputs, and where a specific input gives a distinct output. Another possible description is that the output of an earlier initial gate is potentially connected to the input of another gate.

In the new circuit, the output depends not only on the input, but also on the most recent value of the output. Putting it in a different way, the output of a later gate is connected to the input of an earlier gate. Of course this required a little more analysis than the previous circuits we’ve taken up, to be able to get the truth tables, and to determine its significance.

For the simpler (and historically older) two-input flip-flops, I first had to show them the designation of the two outputs, that for most of the possible inputs they are opposite, so they have been labeled as complements.

Since this means that the one input that produces the output not fitting the definition has to be prevented. It also meant that in the truth table certain inputs can provide different outputs depending on the previous state.

From there I proceeded to a one-input flip-flop, and one that relied on a clock pulse to change values, that was supposed to give a limit as to when a flip flop can, well, flip or flop. This two-input flip-flop had two indeterminate or invalid states, which was removed in the next example.

I also had to change their mindset about the one-input flip flop where in the truth table the present state of the output is in the left side and the next state on the right side. Instead of calling it the same as one of the gates they learned, they had to be told, for example, that having a value of zero, the old output is retained, while when it is one, it is inversed.

In the end I told them it was used in the memory of computers.

Session 1037 got an invalid or indeterminate state. Class dismissed.