In digital circuit design, especially in microprocessor or measuring applications, generating a clock signal often involves dividing a master clock. The proposed 4-chip solution presented here is highly adaptable. It takes a 50% duty cycle input clock and produces a selectable 50% duty cycle clock (determined by an 8-way DIP switch) for divisors ranging from 1 to 255. The central component of this design is IC1, an 8-bit down-counter, programmed by the binary configuration set on the eight DIP switches. Additionally, an edge detector circuit composed of IC3 and IC4 generates pulses at each rising and falling edge of the input clock, denoted as f0.
Clock Signal Generation: Toggle Mechanism
Upon reaching zero, the counter triggers a flip flop, creating an output signal with a 50:50 mark/space ratio. The specific gate configurations in the edge detector are crucial, ensuring the correct number of gates and appropriate delay times.
Importance of Propagation Delay: Ensuring Reliable Clocking
The total propagation delay, indicating the time taken for a signal at a gate’s input to influence the output, is crucial. Seven HC type gates are utilized to generate a pulse with sufficient width to effectively clock the counter. This delay is detailed in the data sheet for reference.
Edge Detector Functionality: Dual Pulse Generation
The edge detector produces pulses on both positive and negative edges of the input clock signal. Each clock impulse on CP decrements the down-counter value. Upon reaching zero, the terminal count pin (TC) generates a negative pulse. This pulse reloads the counter (via parallel load PL) based on the binary switch setting, allowing continuous counting from the reloaded value.
Flip Flop Configuration: Toggle Flip Flop Operation
The JK flip flop (IC3) is set up as a toggle flip flop, where both inputs J and K are connected to ‘1’. With this configuration, the outputs Q and Q change state (toggle) upon each rising edge of the TC output from IC1.
Setting the Division Ratio: Utilizing DIP Switches
The DIP switches play a pivotal role in setting the division ratio. For instance, to divide the clock signal by 23, the DIP switches are configured to the binary value of 23 (00010111), with specific switches like P4, P2, P1, and P0 set to ‘High’. This setup enables precise control over the division process.