First Assessment

A project log for 555ENabled Microprocessor

A Microprocesser made in a digital logic family based on the NE555

TimTim 12/05/2021 at 10:070 Comments

Ok, I may have played around with the NE555 years ago and also owned some kind of circuit book for it.  But I always only copied circuits from somewhere else. So, time to study its details a bit more. It's not my first obscure logic style, so we ought to find something, right?

The block diagram of the N555 from the TI datasheet is shown above. What do we get on a functional level? Two comparators with fixed thresholds, an RS flipflop with reset input and an output driver. The threshold input should be good to act as switch for an analog summing input network and the RS flipflop could become part of a latch. This does not look too bad. CONT and DISCH are probably not too useful for logic circuits, but we will see.

The functionality is described as this in the datasheet:

I don't get why the RESET voltage threshold is not listed. Luckily it is defined later in the datasheet:

A minimum of 0.3V appears quite low. This means that no diodes or anything causing a large voltage drop may be between the reset input and ground. Something to keep in mind for later.

Ok, all in all this does not look too bad. We can probably construct both registers and combinatoric logic out of the NE555 and some additional components. In the mean time I also found some NE555 lying around. So let's get to some experiments.