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 my two hour session for the Interfacing Computer Systems course for the sixth week of classes, because of the possibility that there would be peer evaluators stepping in at any time, I had to come up with a lecture for the entire time.

It wasn’t difficult though. Since we were talking about the parallel port and they already took up gates, buffers, multiplex chips and such in their switching theory lecture subject last term, I went on to one of the more complicated programming peripheral interface chips being used, the 8255A.

I started, of course, with identifying the forty-pin configuration of the integrated circuit.

And to add some interaction into the session, at that point I asked them that based on our first lecture, how many data buses were in the chip.

From there I went into the four types of data transfer: the simple I/O, the strobe I/O, the simple handshake and the double handshake.

The first just sends the data.

The second activates a bit at the same time telling the receiving component that data is ready to be read from its bus.

The third has the sending component wait immediately afterwards for another bit activation acknowledging the receipt of the data.

The fourth goes further and sees the deactivation of the acknowledgement bit as meaning that new data can now be received.

From there I went into the basic operations of the chip, which are connecting the main data port to one of the three other ports for one way transfer, vice versa, or the data port sending to the control byte – which allows for more complex operations.

I detailed what each bit of the control byte entails – that port A would be input or output, same with port B, and they could set the lower four and upper four bits of port C differently. Next, there was also a mode to each operation to be set, based on the four types of transfer I mentioned earlier.

There was a last bit, that when active sets the mode of operation. But when set to a low voltage, the other bits of the control word can give the specifics to assign value to one of the eight bits of Port C.

One of my co-teachers arrived, but this was when we were already finished with the lecture. I’m sure another class of mine will be visited.

Session 815 didn’t show up in my lecture. Class dismissed.