Dynamic Functions
The logic gates we have presented so far are static. The output reflexes the state of the input pins. This is significant but does not allow a controlled response to the stimuli. This requires a master clock to regulate data transfers. A simple master clock is an AND circuit with one leg always +. The other input is feedback from the output thru a NOT inverter. The output being negative makes the bottom input positive, which makes the output positive, making the input negative. In other words, the circuit turns itself off and on. A blue dot indicates a TRUE (+) signal and a red dot a FALSE.
The cycle time and the ratio of the + and – levels would be determined by the physical properties of the logic gates. They can be easily adjusted by two static elements discussed elsewhere – resistors and capacitors. If we place a resistor and capacitor following the inverter in the above diagram it will delay the time that the signal will change from – to +. For example, when the output from the inverter goes from 0 volts to 1 volt, the resistor would slowly charge the capacitor to 1 volt, which in turn would make the bottom input to the AND circuit +. RC time constant – Wikipedia Many natural elements have resistance and capacitance properties.
This timed pulse can be used to capture and “step” data thru a series of logic gates allowing analysis and response to changes in input signals. Flip-flop (electronics) – Wikipedia
In the diagram below, the data would be connected to the R input and the clock signal to the S. Aclock pulse would capture the state of the R input which would stay the same until the next clock cycle. This “machine” cycle is the basis for moving data thru a computing device. The output Q would be the input to the next logic element and the next clock cycle would move the data forward. Shift register – Wikipedia
A simple computing sequence would be
- Capture the state of the input signals
- Use logic gates to calculate the desired output based on the inputs
- Use logic gates to send the output to an Actuator – Wikipedia
- Repeat the process adjusting for changes in the inputs
Clock control permits an organized way to examine data. Basic computer architecture normally requires two data inputs and an instruction type (add, compare, store).
Next Chapter – Analysis
